Update version

Closes #19

.github/FUNDING.yml

@@ -1,4 +1,3 @@
 github: Tyrrrz
 patreon: Tyrrrz
-open_collective: Tyrrrz
-custom: ['buymeacoffee.com/Tyrrrz']
+custom: ['buymeacoffee.com/Tyrrrz', 'tyrrrz.me/donate']

.github/workflows/CD.yml

@@ -0,0 +1,25 @@
+name: CD
+
+on:
+  push:
+    tags:
+    - '*'
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v1
+
+    - name: Install .NET Core
+      uses: actions/setup-dotnet@v1
+      with:
+        dotnet-version: 3.1.100
+
+    - name: Pack
+      run: dotnet pack CliFx --configuration Release
+
+    - name: Deploy
+      run: dotnet nuget push CliFx/bin/Release/*.nupkg -s nuget.org -k ${{secrets.NUGET_TOKEN}}

.github/workflows/CI.yml

@@ -0,0 +1,22 @@
+name: CI
+
+on: [push, pull_request]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v1
+
+    - name: Install .NET Core
+      uses: actions/setup-dotnet@v1
+      with:
+        dotnet-version: 3.1.100
+
+    - name: Build & test
+      run: dotnet test --configuration Release
+
+    - name: Coverage
+      run: curl -s https://codecov.io/bash | bash -s -- -f CliFx.Tests/bin/Release/Coverage.xml -t ${{secrets.CODECOV_TOKEN}} -Z

.gitignore

@@ -143,6 +143,7 @@ _TeamCity*
 _NCrunch_*
 .*crunch*.local.xml
 nCrunchTemp_*
+.ncrunchsolution
 
 # MightyMoose
 *.mm.*

CliFx.Benchmarks/Benchmark.cs

@@ -1,34 +1,46 @@
 using System.Threading.Tasks;
 using BenchmarkDotNet.Attributes;
+using BenchmarkDotNet.Order;
 using CliFx.Benchmarks.Commands;
+using CommandLine;
 
 namespace CliFx.Benchmarks
 {
-    [CoreJob]
+    [SimpleJob]
     [RankColumn]
+    [Orderer(SummaryOrderPolicy.FastestToSlowest)]
     public class Benchmark
     {
         private static readonly string[] Arguments = {"--str", "hello world", "-i", "13", "-b"};
 
         [Benchmark(Description = "CliFx", Baseline = true)]
-        public Task<int> ExecuteWithCliFx() => new CliApplicationBuilder().AddCommand(typeof(CliFxCommand)).Build().RunAsync(Arguments);
+        public async ValueTask<int> ExecuteWithCliFx() =>
+            await new CliApplicationBuilder().AddCommand(typeof(CliFxCommand)).Build().RunAsync(Arguments);
 
         [Benchmark(Description = "System.CommandLine")]
-        public Task<int> ExecuteWithSystemCommandLine() => new SystemCommandLineCommand().ExecuteAsync(Arguments);
+        public async Task<int> ExecuteWithSystemCommandLine() =>
+            await new SystemCommandLineCommand().ExecuteAsync(Arguments);
 
         [Benchmark(Description = "McMaster.Extensions.CommandLineUtils")]
-        public int ExecuteWithMcMaster() => McMaster.Extensions.CommandLineUtils.CommandLineApplication.Execute<McMasterCommand>(Arguments);
+        public int ExecuteWithMcMaster() =>
+            McMaster.Extensions.CommandLineUtils.CommandLineApplication.Execute<McMasterCommand>(Arguments);
 
-        // Skipped because this benchmark freezes after a couple of iterations
-        // Probably wasn't designed to run multiple times in single process execution
-        //[Benchmark(Description = "CommandLineParser")]
-        public void ExecuteWithCommandLineParser()
-        {
-            var parsed = CommandLine.Parser.Default.ParseArguments(Arguments, typeof(CommandLineParserCommand));
-            CommandLine.ParserResultExtensions.WithParsed<CommandLineParserCommand>(parsed, c => c.Execute());
-        }
+        [Benchmark(Description = "CommandLineParser")]
+        public void ExecuteWithCommandLineParser() =>
+            new Parser()
+                .ParseArguments(Arguments, typeof(CommandLineParserCommand))
+                .WithParsed<CommandLineParserCommand>(c => c.Execute());
 
         [Benchmark(Description = "PowerArgs")]
-        public void ExecuteWithPowerArgs() => PowerArgs.Args.InvokeMain<PowerArgsCommand>(Arguments);
+        public void ExecuteWithPowerArgs() =>
+            PowerArgs.Args.InvokeMain<PowerArgsCommand>(Arguments);
+
+        [Benchmark(Description = "Clipr")]
+        public void ExecuteWithClipr() =>
+            clipr.CliParser.Parse<CliprCommand>(Arguments).Execute();
+
+        [Benchmark(Description = "Cocona")]
+        public void ExecuteWithCocona() =>
+            Cocona.CoconaApp.Run<CoconaCommand>(Arguments);
     }
 }

CliFx.Benchmarks/CliFx.Benchmarks.csproj

@@ -1,15 +1,17 @@
 <Project Sdk="Microsoft.NET.Sdk">
+  <Import Project="../CliFx.props" />
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFramework>netcoreapp2.2</TargetFramework>
-    <LangVersion>latest</LangVersion>
+    <TargetFramework>netcoreapp3.1</TargetFramework>
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="BenchmarkDotNet" Version="0.11.5" />
-    <PackageReference Include="CommandLineParser" Version="2.6.0" />
-    <PackageReference Include="McMaster.Extensions.CommandLineUtils" Version="2.3.4" />
+    <PackageReference Include="BenchmarkDotNet" Version="0.12.0" />
+    <PackageReference Include="clipr" Version="1.6.1" />
+    <PackageReference Include="Cocona" Version="1.0.0" />
+    <PackageReference Include="CommandLineParser" Version="2.7.82" />
+    <PackageReference Include="McMaster.Extensions.CommandLineUtils" Version="2.5.0" />
     <PackageReference Include="PowerArgs" Version="3.6.0" />
     <PackageReference Include="System.CommandLine.Experimental" Version="0.3.0-alpha.19317.1" />
   </ItemGroup>

CliFx.Benchmarks/Commands/CliFxCommand.cs

@@ -1,6 +1,5 @@
 using System.Threading.Tasks;
 using CliFx.Attributes;
-using CliFx.Services;
 
 namespace CliFx.Benchmarks.Commands
 {
@@ -8,7 +7,7 @@ namespace CliFx.Benchmarks.Commands
     public class CliFxCommand : ICommand
     {
         [CommandOption("str", 's')]
-        public string StrOption { get; set; }
+        public string? StrOption { get; set; }
 
         [CommandOption("int", 'i')]
         public int IntOption { get; set; }
@@ -16,6 +15,6 @@ namespace CliFx.Benchmarks.Commands
         [CommandOption("bool", 'b')]
         public bool BoolOption { get; set; }
 
-        public Task ExecuteAsync(IConsole console) => Task.CompletedTask;
+        public ValueTask ExecuteAsync(IConsole console) => default;
     }
 }

CliFx.Benchmarks/Commands/CliprCommand.cs

@@ -0,0 +1,20 @@
+using clipr;
+
+namespace CliFx.Benchmarks.Commands
+{
+    public class CliprCommand
+    {
+        [NamedArgument('s', "str")]
+        public string? StrOption { get; set; }
+
+        [NamedArgument('i', "int")]
+        public int IntOption { get; set; }
+
+        [NamedArgument('b', "bool", Constraint = NumArgsConstraint.Optional, Const = true)]
+        public bool BoolOption { get; set; }
+
+        public void Execute()
+        {
+        }
+    }
+}

CliFx.Benchmarks/Commands/CoconaCommand.cs

@@ -0,0 +1,17 @@
+using Cocona;
+
+namespace CliFx.Benchmarks.Commands
+{
+    public class CoconaCommand
+    {
+        public void Execute(
+            [Option("str", new []{'s'})]
+            string? strOption,
+            [Option("int", new []{'i'})]
+            int intOption,
+            [Option("bool", new []{'b'})]
+            bool boolOption)
+        {
+        }
+    }
+}

CliFx.Benchmarks/Commands/CommandLineParserCommand.cs

@@ -5,7 +5,7 @@ namespace CliFx.Benchmarks.Commands
     public class CommandLineParserCommand
     {
         [Option('s', "str")]
-        public string StrOption { get; set; }
+        public string? StrOption { get; set; }
 
         [Option('i', "int")]
         public int IntOption { get; set; }

CliFx.Benchmarks/Commands/McMasterCommand.cs

@@ -5,7 +5,7 @@ namespace CliFx.Benchmarks.Commands
     public class McMasterCommand
     {
         [Option("--str|-s")]
-        public string StrOption { get; set; }
+        public string? StrOption { get; set; }
 
         [Option("--int|-i")]
         public int IntOption { get; set; }

CliFx.Benchmarks/Commands/PowerArgsCommand.cs

@@ -5,7 +5,7 @@ namespace CliFx.Benchmarks.Commands
     public class PowerArgsCommand
     {
         [ArgShortcut("--str"), ArgShortcut("-s")]
-        public string StrOption { get; set; }
+        public string? StrOption { get; set; }
 
         [ArgShortcut("--int"), ArgShortcut("-i")]
         public int IntOption { get; set; }

CliFx.Benchmarks/Commands/SystemCommandLineCommand.cs

@@ -14,7 +14,7 @@ namespace CliFx.Benchmarks.Commands
             {
                 new Option(new[] {"--str", "-s"})
                 {
-                    Argument = new Argument<string>()
+                    Argument = new Argument<string?>()
                 },
                 new Option(new[] {"--int", "-i"})
                 {

CliFx.Demo/CliFx.Demo.csproj

@@ -1,14 +1,14 @@
 <Project Sdk="Microsoft.NET.Sdk">
+  <Import Project="../CliFx.props" />
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFramework>netcoreapp2.2</TargetFramework>
-    <LangVersion>latest</LangVersion>
+    <TargetFramework>netcoreapp3.1</TargetFramework>
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.Extensions.DependencyInjection" Version="2.2.0" />
-    <PackageReference Include="Newtonsoft.Json" Version="12.0.2" />
+    <PackageReference Include="Microsoft.Extensions.DependencyInjection" Version="3.1.1" />
+    <PackageReference Include="Newtonsoft.Json" Version="12.0.3" />
   </ItemGroup>
 
   <ItemGroup>

CliFx.Demo/Commands/BookAddCommand.cs

@@ -5,7 +5,6 @@ using CliFx.Demo.Internal;
 using CliFx.Demo.Models;
 using CliFx.Demo.Services;
 using CliFx.Exceptions;
-using CliFx.Services;
 
 namespace CliFx.Demo.Commands
 {
@@ -14,31 +13,25 @@ namespace CliFx.Demo.Commands
     {
         private readonly LibraryService _libraryService;
 
-        [CommandOption("title", 't', IsRequired = true, Description = "Book title.")]
-        public string Title { get; set; }
+        [CommandParameter(0, Name = "title", Description = "Book title.")]
+        public string Title { get; set; } = "";
 
         [CommandOption("author", 'a', IsRequired = true, Description = "Book author.")]
-        public string Author { get; set; }
+        public string Author { get; set; } = "";
 
         [CommandOption("published", 'p', Description = "Book publish date.")]
-        public DateTimeOffset Published { get; set; }
+        public DateTimeOffset Published { get; set; } = CreateRandomDate();
 
         [CommandOption("isbn", 'n', Description = "Book ISBN.")]
-        public Isbn Isbn { get; set; }
+        public Isbn Isbn { get; set; } = CreateRandomIsbn();
 
         public BookAddCommand(LibraryService libraryService)
         {
             _libraryService = libraryService;
         }
 
-        public Task ExecuteAsync(IConsole console)
+        public ValueTask ExecuteAsync(IConsole console)
         {
-            // To make the demo simpler, we will just generate random publish date and ISBN if they were not set
-            if (Published == default)
-                Published = CreateRandomDate();
-            if (Isbn == default)
-                Isbn = CreateRandomIsbn();
-
             if (_libraryService.GetBook(Title) != null)
                 throw new CommandException("Book already exists.", 1);
 
@@ -48,7 +41,7 @@ namespace CliFx.Demo.Commands
             console.Output.WriteLine("Book added.");
             console.RenderBook(book);
 
-            return Task.CompletedTask;
+            return default;
         }
     }
 
@@ -65,7 +58,7 @@ namespace CliFx.Demo.Commands
             Random.Next(1, 59),
             TimeSpan.Zero);
 
-        public static Isbn CreateRandomIsbn() => new Isbn(
+        private static Isbn CreateRandomIsbn() => new Isbn(
             Random.Next(0, 999),
             Random.Next(0, 99),
             Random.Next(0, 99999),

CliFx.Demo/Commands/BookCommand.cs

@@ -3,7 +3,6 @@ using CliFx.Attributes;
 using CliFx.Demo.Internal;
 using CliFx.Demo.Services;
 using CliFx.Exceptions;
-using CliFx.Services;
 
 namespace CliFx.Demo.Commands
 {
@@ -12,15 +11,15 @@ namespace CliFx.Demo.Commands
     {
         private readonly LibraryService _libraryService;
 
-        [CommandOption("title", 't', IsRequired = true, Description = "Book title.")]
-        public string Title { get; set; }
+        [CommandParameter(0, Name = "title", Description = "Book title.")]
+        public string Title { get; set; } = "";
 
         public BookCommand(LibraryService libraryService)
         {
             _libraryService = libraryService;
         }
 
-        public Task ExecuteAsync(IConsole console)
+        public ValueTask ExecuteAsync(IConsole console)
         {
             var book = _libraryService.GetBook(Title);
 
@@ -29,7 +28,7 @@ namespace CliFx.Demo.Commands
 
             console.RenderBook(book);
 
-            return Task.CompletedTask;
+            return default;
         }
     }
 }

CliFx.Demo/Commands/BookListCommand.cs

@@ -2,7 +2,6 @@
 using CliFx.Attributes;
 using CliFx.Demo.Internal;
 using CliFx.Demo.Services;
-using CliFx.Services;
 
 namespace CliFx.Demo.Commands
 {
@@ -16,7 +15,7 @@ namespace CliFx.Demo.Commands
             _libraryService = libraryService;
         }
 
-        public Task ExecuteAsync(IConsole console)
+        public ValueTask ExecuteAsync(IConsole console)
         {
             var library = _libraryService.GetLibrary();
 
@@ -32,7 +31,7 @@ namespace CliFx.Demo.Commands
                 console.RenderBook(book);
             }
 
-            return Task.CompletedTask;
+            return default;
         }
     }
 }

CliFx.Demo/Commands/BookRemoveCommand.cs

@@ -2,7 +2,6 @@
 using CliFx.Attributes;
 using CliFx.Demo.Services;
 using CliFx.Exceptions;
-using CliFx.Services;
 
 namespace CliFx.Demo.Commands
 {
@@ -11,15 +10,15 @@ namespace CliFx.Demo.Commands
     {
         private readonly LibraryService _libraryService;
 
-        [CommandOption("title", 't', IsRequired = true, Description = "Book title.")]
-        public string Title { get; set; }
+        [CommandParameter(0, Name = "title", Description = "Book title.")]
+        public string Title { get; set; } = "";
 
         public BookRemoveCommand(LibraryService libraryService)
         {
             _libraryService = libraryService;
         }
 
-        public Task ExecuteAsync(IConsole console)
+        public ValueTask ExecuteAsync(IConsole console)
         {
             var book = _libraryService.GetBook(Title);
 
@@ -30,7 +29,7 @@ namespace CliFx.Demo.Commands
 
             console.Output.WriteLine($"Book {Title} removed.");
 
-            return Task.CompletedTask;
+            return default;
         }
     }
 }

CliFx.Demo/Internal/Extensions.cs

@@ -1,6 +1,5 @@
 using System;
 using CliFx.Demo.Models;
-using CliFx.Services;
 
 namespace CliFx.Demo.Internal
 {

CliFx.Demo/Models/Isbn.cs

@@ -1,5 +1,4 @@
 using System;
-using System.Globalization;
 
 namespace CliFx.Demo.Models
 {
@@ -24,21 +23,23 @@ namespace CliFx.Demo.Models
             CheckDigit = checkDigit;
         }
 
-        public override string ToString() => $"{EanPrefix:000}-{RegistrationGroup:00}-{Registrant:00000}-{Publication:00}-{CheckDigit:0}";
+        public override string ToString() =>
+            $"{EanPrefix:000}-{RegistrationGroup:00}-{Registrant:00000}-{Publication:00}-{CheckDigit:0}";
     }
 
     public partial class Isbn
     {
-        public static Isbn Parse(string value)
+        public static Isbn Parse(string value, IFormatProvider formatProvider)
         {
             var components = value.Split('-', 5, StringSplitOptions.RemoveEmptyEntries);
 
             return new Isbn(
-                int.Parse(components[0], CultureInfo.InvariantCulture),
-                int.Parse(components[1], CultureInfo.InvariantCulture),
-                int.Parse(components[2], CultureInfo.InvariantCulture),
-                int.Parse(components[3], CultureInfo.InvariantCulture),
-                int.Parse(components[4], CultureInfo.InvariantCulture));
+                int.Parse(components[0], formatProvider),
+                int.Parse(components[1], formatProvider),
+                int.Parse(components[2], formatProvider),
+                int.Parse(components[3], formatProvider),
+                int.Parse(components[4], formatProvider)
+            );
         }
     }
 }

CliFx.Demo/Program.cs

@@ -1,4 +1,5 @@
-using System.Threading.Tasks;
+using System;
+using System.Threading.Tasks;
 using CliFx.Demo.Commands;
 using CliFx.Demo.Services;
 using Microsoft.Extensions.DependencyInjection;
@@ -7,7 +8,7 @@ namespace CliFx.Demo
 {
     public static class Program
     {
-        public static Task<int> Main(string[] args)
+        private static IServiceProvider GetServiceProvider()
         {
             // We use Microsoft.Extensions.DependencyInjection for injecting dependencies in commands
             var services = new ServiceCollection();
@@ -21,13 +22,14 @@ namespace CliFx.Demo
             services.AddTransient<BookRemoveCommand>();
             services.AddTransient<BookListCommand>();
 
-            var serviceProvider = services.BuildServiceProvider();
+            return services.BuildServiceProvider();
+        }
 
-            return new CliApplicationBuilder()
+        public static async Task<int> Main() =>
+            await new CliApplicationBuilder()
                 .AddCommandsFromThisAssembly()
-                .UseCommandFactory(schema => (ICommand) serviceProvider.GetRequiredService(schema.Type))
+                .UseTypeActivator(GetServiceProvider().GetService)
                 .Build()
-                .RunAsync(args);
-        }
+                .RunAsync();
     }
 }

CliFx.Demo/Readme.md

@@ -2,6 +2,6 @@
 
 Sample command line interface for managing a library of books.
 
-This demo project shows basic CliFx functionality such as command routing, option parsing, autogenerated help text, and some other things.
+This demo project shows basic CliFx functionality such as command routing, argument parsing, autogenerated help text, and some other things.
 
 You can get a list of available commands by running `CliFx.Demo --help`.

CliFx.Demo/Services/LibraryService.cs

@@ -25,7 +25,7 @@ namespace CliFx.Demo.Services
             return JsonConvert.DeserializeObject<Library>(data);
         }
 
-        public Book GetBook(string title) => GetLibrary().Books.FirstOrDefault(b => b.Title == title);
+        public Book? GetBook(string title) => GetLibrary().Books.FirstOrDefault(b => b.Title == title);
 
         public void AddBook(Book book)
         {

CliFx.Tests.Dummy/CliFx.Tests.Dummy.csproj

@@ -1,10 +1,9 @@
 <Project Sdk="Microsoft.NET.Sdk">
+  <Import Project="../CliFx.props" />
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFramework>net46</TargetFramework>
-    <Version>1.2.3.4</Version>
-    <LangVersion>latest</LangVersion>
+    <TargetFramework>netcoreapp3.1</TargetFramework>
   </PropertyGroup>
 
   <ItemGroup>

CliFx.Tests.Dummy/Commands/GreeterCommand.cs

@@ -1,31 +0,0 @@
-using System.Text;
-using System.Threading.Tasks;
-using CliFx.Attributes;
-using CliFx.Services;
-
-namespace CliFx.Tests.Dummy.Commands
-{
-    [Command]
-    public class GreeterCommand : ICommand
-    {
-        [CommandOption("target", 't', Description = "Greeting target.")]
-        public string Target { get; set; } = "world";
-
-        [CommandOption('e', Description = "Whether the greeting should be exclaimed.")]
-        public bool IsExclaimed { get; set; }
-
-        public Task ExecuteAsync(IConsole console)
-        {
-            var buffer = new StringBuilder();
-
-            buffer.Append("Hello").Append(' ').Append(Target);
-
-            if (IsExclaimed)
-                buffer.Append('!');
-
-            console.Output.WriteLine(buffer.ToString());
-
-            return Task.CompletedTask;
-        }
-    }
-}

CliFx.Tests.Dummy/Commands/HelloWorldCommand.cs

@@ -0,0 +1,19 @@
+using System.Threading.Tasks;
+using CliFx.Attributes;
+
+namespace CliFx.Tests.Dummy.Commands
+{
+    [Command]
+    public class HelloWorldCommand : ICommand
+    {
+        [CommandOption("target", EnvironmentVariableName = "ENV_TARGET")]
+        public string Target { get; set; } = "World";
+
+        public ValueTask ExecuteAsync(IConsole console)
+        {
+            console.Output.WriteLine($"Hello {Target}!");
+
+            return default;
+        }
+    }
+}

CliFx.Tests.Dummy/Commands/LogCommand.cs

@@ -1,25 +0,0 @@
-using System;
-using System.Threading.Tasks;
-using CliFx.Attributes;
-using CliFx.Services;
-
-namespace CliFx.Tests.Dummy.Commands
-{
-    [Command("log", Description = "Calculate the logarithm of a value.")]
-    public class LogCommand : ICommand
-    {
-        [CommandOption("value", 'v', IsRequired = true, Description = "Value whose logarithm is to be found.")]
-        public double Value { get; set; }
-
-        [CommandOption("base", 'b', Description = "Logarithm base.")]
-        public double Base { get; set; } = 10;
-
-        public Task ExecuteAsync(IConsole console)
-        {
-            var result = Math.Log(Value, Base);
-            console.Output.WriteLine(result);
-
-            return Task.CompletedTask;
-        }
-    }
-}

CliFx.Tests.Dummy/Commands/SumCommand.cs

@@ -1,23 +0,0 @@
-using System.Collections.Generic;
-using System.Linq;
-using System.Threading.Tasks;
-using CliFx.Attributes;
-using CliFx.Services;
-
-namespace CliFx.Tests.Dummy.Commands
-{
-    [Command("sum", Description = "Calculate the sum of all input values.")]
-    public class SumCommand : ICommand
-    {
-        [CommandOption("values", 'v', IsRequired = true, Description = "Input values.")]
-        public IReadOnlyList<double> Values { get; set; }
-
-        public Task ExecuteAsync(IConsole console)
-        {
-            var result = Values.Sum();
-            console.Output.WriteLine(result);
-
-            return Task.CompletedTask;
-        }
-    }
-}

CliFx.Tests.Dummy/Program.cs

@@ -1,21 +1,13 @@
-using System.Globalization;
-using System.Threading.Tasks;
+using System.Threading.Tasks;
 
 namespace CliFx.Tests.Dummy
 {
-    public static class Program
+    public class Program
     {
-        public static Task<int> Main(string[] args)
-        {
-            // Set culture to invariant to maintain consistent format because we rely on it in tests
-            CultureInfo.DefaultThreadCurrentCulture = CultureInfo.InvariantCulture;
-            CultureInfo.DefaultThreadCurrentUICulture = CultureInfo.InvariantCulture;
-
-            return new CliApplicationBuilder()
+        public static async Task Main() =>
+            await new CliApplicationBuilder()
                 .AddCommandsFromThisAssembly()
-                .UseDescription("Dummy program used for E2E tests.")
                 .Build()
-                .RunAsync(args);
-        }
+                .RunAsync();
     }
 }

CliFx.Tests/CliApplicationBuilderTests.cs

@@ -0,0 +1,45 @@
+using NUnit.Framework;
+using System;
+using System.IO;
+using CliFx.Tests.TestCommands;
+
+namespace CliFx.Tests
+{
+    [TestFixture]
+    public class CliApplicationBuilderTests
+    {
+        [Test(Description = "All builder methods must return without exceptions")]
+        public void Smoke_Test()
+        {
+            // Arrange
+            var builder = new CliApplicationBuilder();
+
+            // Act
+            builder
+                .AddCommand(typeof(HelloWorldDefaultCommand))
+                .AddCommandsFrom(typeof(HelloWorldDefaultCommand).Assembly)
+                .AddCommands(new[] {typeof(HelloWorldDefaultCommand)})
+                .AddCommandsFrom(new[] {typeof(HelloWorldDefaultCommand).Assembly})
+                .AddCommandsFromThisAssembly()
+                .AllowDebugMode()
+                .AllowPreviewMode()
+                .UseTitle("test")
+                .UseExecutableName("test")
+                .UseVersionText("test")
+                .UseDescription("test")
+                .UseConsole(new VirtualConsole(TextWriter.Null))
+                .UseTypeActivator(Activator.CreateInstance)
+                .Build();
+        }
+
+        [Test(Description = "Builder must be able to produce an application when no parameters are specified")]
+        public void Build_Test()
+        {
+            // Arrange
+            var builder = new CliApplicationBuilder();
+
+            // Act
+            builder.Build();
+        }
+    }
+}

CliFx.Tests/CliApplicationTests.Commands.cs

@@ -1,53 +0,0 @@
-using System;
-using System.Threading.Tasks;
-using CliFx.Attributes;
-using CliFx.Exceptions;
-using CliFx.Services;
-
-namespace CliFx.Tests
-{
-    public partial class CliApplicationTests
-    {
-        [Command]
-        private class DefaultCommand : ICommand
-        {
-            public Task ExecuteAsync(IConsole console)
-            {
-                console.Output.WriteLine("DefaultCommand executed.");
-                return Task.CompletedTask;
-            }
-        }
-
-        [Command("cmd")]
-        private class NamedCommand : ICommand
-        {
-            public Task ExecuteAsync(IConsole console)
-            {
-                console.Output.WriteLine("NamedCommand executed.");
-                return Task.CompletedTask;
-            }
-        }
-    }
-
-    // Negative
-    public partial class CliApplicationTests
-    {
-        [Command("faulty1")]
-        private class FaultyCommand1 : ICommand
-        {
-            public Task ExecuteAsync(IConsole console) => throw new CommandException(150);
-        }
-
-        [Command("faulty2")]
-        private class FaultyCommand2 : ICommand
-        {
-            public Task ExecuteAsync(IConsole console) => throw new CommandException("FaultyCommand2 error message.", 150);
-        }
-
-        [Command("faulty3")]
-        private class FaultyCommand3 : ICommand
-        {
-            public Task ExecuteAsync(IConsole console) => throw new Exception("FaultyCommand3 error message.");
-        }
-    }
-}

CliFx.Tests/CliApplicationTests.cs

@@ -1,76 +1,125 @@
-using System;
+using FluentAssertions;
+using NUnit.Framework;
+using System;
 using System.Collections.Generic;
 using System.IO;
+using System.Threading;
 using System.Threading.Tasks;
-using CliFx.Services;
-using FluentAssertions;
-using NUnit.Framework;
+using CliFx.Tests.TestCommands;
 
 namespace CliFx.Tests
 {
     [TestFixture]
-    public partial class CliApplicationTests
+    public class CliApplicationTests
     {
+        private const string TestAppName = "TestApp";
+        private const string TestVersionText = "v1.0";
+
         private static IEnumerable<TestCaseData> GetTestCases_RunAsync()
         {
             yield return new TestCaseData(
-                new[] {typeof(DefaultCommand)},
+                new[] {typeof(HelloWorldDefaultCommand)},
                 new string[0],
-                "DefaultCommand executed."
+                new Dictionary<string, string>(),
+                "Hello world."
             );
 
             yield return new TestCaseData(
-                new[] {typeof(NamedCommand)},
-                new[] {"cmd"},
-                "NamedCommand executed."
-            );
-        }
-
-        private static IEnumerable<TestCaseData> GetTestCases_HelpAndVersion_RunAsync()
-        {
-            yield return new TestCaseData(
-                new[] {typeof(DefaultCommand)},
-                new string[0]
+                new[] {typeof(ConcatCommand)},
+                new[] {"concat", "-i", "foo", "-i", "bar", "-s", " "},
+                new Dictionary<string, string>(),
+                "foo bar"
             );
 
             yield return new TestCaseData(
-                new[] {typeof(DefaultCommand)},
-                new[] {"-h"}
+                new[] {typeof(ConcatCommand)},
+                new[] {"concat", "-i", "one", "two", "three", "-s", ", "},
+                new Dictionary<string, string>(),
+                "one, two, three"
             );
 
             yield return new TestCaseData(
-                new[] {typeof(DefaultCommand)},
-                new[] {"--help"}
+                new[] {typeof(DivideCommand)},
+                new[] {"div", "-D", "24", "-d", "8"},
+                new Dictionary<string, string>(),
+                "3"
             );
 
             yield return new TestCaseData(
-                new[] {typeof(DefaultCommand)},
-                new[] {"--version"}
+                new[] {typeof(HelloWorldDefaultCommand)},
+                new[] {"--version"},
+                new Dictionary<string, string>(),
+                TestVersionText
             );
 
             yield return new TestCaseData(
-                new[] {typeof(NamedCommand)},
-                new string[0]
+                new[] {typeof(ConcatCommand)},
+                new[] {"--version"},
+                new Dictionary<string, string>(),
+                TestVersionText
             );
 
             yield return new TestCaseData(
-                new[] {typeof(NamedCommand)},
-                new[] {"cmd", "-h"}
+                new[] {typeof(ConcatCommand)},
+                new string[0],
+                new Dictionary<string, string>(),
+                null
             );
 
             yield return new TestCaseData(
-                new[] {typeof(FaultyCommand1)},
-                new[] {"faulty1", "-h"}
+                new[] {typeof(ConcatCommand)},
+                new[] {"-h"},
+                new Dictionary<string, string>(),
+                null
             );
 
             yield return new TestCaseData(
-                new[] {typeof(FaultyCommand2)},
-                new[] {"faulty2", "-h"}
+                new[] {typeof(ConcatCommand)},
+                new[] {"--help"},
+                new Dictionary<string, string>(),
+                null
             );
 
             yield return new TestCaseData(
-                new[] {typeof(FaultyCommand3)},
-                new[] {"faulty3", "-h"}
+                new[] {typeof(ConcatCommand)},
+                new[] {"concat", "-h"},
+                new Dictionary<string, string>(),
+                null
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(ExceptionCommand)},
+                new[] {"exc", "-h"},
+                new Dictionary<string, string>(),
+                null
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(CommandExceptionCommand)},
+                new[] {"exc", "-h"},
+                new Dictionary<string, string>(),
+                null
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(ConcatCommand)},
+                new[] {"[preview]"},
+                new Dictionary<string, string>(),
+                null
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(ExceptionCommand)},
+                new[] {"[preview]", "exc"},
+                new Dictionary<string, string>(),
+                null
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(ConcatCommand)},
+                new[] {"[preview]", "concat", "-o", "value"},
+                new Dictionary<string, string>(),
+                null
             );
         }
 
@@ -78,97 +127,325 @@ namespace CliFx.Tests
         {
             yield return new TestCaseData(
                 new Type[0],
-                new string[0]
+                new string[0],
+                new Dictionary<string, string>(),
+                null, null
             );
 
             yield return new TestCaseData(
-                new[] {typeof(DefaultCommand)},
-                new[] {"non-existing"}
+                new[] {typeof(ConcatCommand)},
+                new[] {"non-existing"},
+                new Dictionary<string, string>(),
+                null, null
             );
 
             yield return new TestCaseData(
-                new[] {typeof(FaultyCommand1)},
-                new[] {"faulty1"}
+                new[] {typeof(ExceptionCommand)},
+                new[] {"exc"},
+                new Dictionary<string, string>(),
+                null, null
             );
 
             yield return new TestCaseData(
-                new[] {typeof(FaultyCommand2)},
-                new[] {"faulty2"}
+                new[] {typeof(CommandExceptionCommand)},
+                new[] {"exc"},
+                new Dictionary<string, string>(),
+                null, null
             );
 
             yield return new TestCaseData(
-                new[] {typeof(FaultyCommand3)},
-                new[] {"faulty3"}
+                new[] {typeof(CommandExceptionCommand)},
+                new[] {"exc"},
+                new Dictionary<string, string>(),
+                null, null
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(CommandExceptionCommand)},
+                new[] {"exc", "-m", "foo bar"},
+                new Dictionary<string, string>(),
+                "foo bar", null
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(CommandExceptionCommand)},
+                new[] {"exc", "-m", "foo bar", "-c", "666"},
+                new Dictionary<string, string>(),
+                "foo bar", 666
+            );
+        }
+
+        private static IEnumerable<TestCaseData> GetTestCases_RunAsync_Help()
+        {
+            yield return new TestCaseData(
+                new[] {typeof(HelpDefaultCommand), typeof(HelpNamedCommand), typeof(HelpSubCommand)},
+                new[] {"--help"},
+                new[]
+                {
+                    TestVersionText,
+                    "Description",
+                    "HelpDefaultCommand description.",
+                    "Usage",
+                    TestAppName, "[command]", "[options]",
+                    "Options",
+                    "-a|--option-a", "OptionA description.",
+                    "-b|--option-b", "OptionB description.",
+                    "-h|--help", "Shows help text.",
+                    "--version", "Shows version information.",
+                    "Commands",
+                    "cmd", "HelpNamedCommand description.",
+                    "You can run", "to show help on a specific command."
+                }
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(HelpSubCommand)},
+                new[] {"--help"},
+                new[]
+                {
+                    TestVersionText,
+                    "Usage",
+                    TestAppName, "[command]",
+                    "Options",
+                    "-h|--help", "Shows help text.",
+                    "--version", "Shows version information.",
+                    "Commands",
+                    "cmd sub", "HelpSubCommand description.",
+                    "You can run", "to show help on a specific command."
+                }
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(HelpDefaultCommand), typeof(HelpNamedCommand), typeof(HelpSubCommand)},
+                new[] {"cmd", "--help"},
+                new[]
+                {
+                    "Description",
+                    "HelpNamedCommand description.",
+                    "Usage",
+                    TestAppName, "cmd", "[command]", "[options]",
+                    "Options",
+                    "-c|--option-c", "OptionC description.",
+                    "-d|--option-d", "OptionD description.",
+                    "-h|--help", "Shows help text.",
+                    "Commands",
+                    "sub", "HelpSubCommand description.",
+                    "You can run", "to show help on a specific command."
+                }
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(HelpDefaultCommand), typeof(HelpNamedCommand), typeof(HelpSubCommand)},
+                new[] {"cmd", "sub", "--help"},
+                new[]
+                {
+                    "Description",
+                    "HelpSubCommand description.",
+                    "Usage",
+                    TestAppName, "cmd sub", "[options]",
+                    "Options",
+                    "-e|--option-e", "OptionE description.",
+                    "-h|--help", "Shows help text."
+                }
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(ParameterCommand)},
+                new[] {"param", "cmd", "--help"},
+                new[]
+                {
+                    "Description",
+                    "Command using positional parameters",
+                    "Usage",
+                    TestAppName, "param cmd", "<first>", "<parameterb>", "<third list...>", "[options]",
+                    "Parameters",
+                    "* first",
+                    "* parameterb",
+                    "* third list", "A list of numbers",
+                    "Options",
+                    "-o|--option",
+                    "-h|--help", "Shows help text."
+                }
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(AllRequiredOptionsCommand)},
+                new[] {"allrequired", "--help"},
+                new[]
+                {
+                    "Description",
+                    "AllRequiredOptionsCommand description.",
+                    "Usage",
+                    TestAppName, "allrequired --option-f <value> --option-g <value>"
+                }
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(SomeRequiredOptionsCommand)},
+                new[] {"somerequired", "--help"},
+                new[]
+                {
+                    "Description",
+                    "SomeRequiredOptionsCommand description.",
+                    "Usage",
+                    TestAppName, "somerequired --option-f <value> [options]"
+                }
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(EnvironmentVariableCommand)},
+                new[] {"--help"},
+                new[]
+                {
+                    "Environment variable:", "ENV_SINGLE_VALUE"
+                }
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(ConcatCommand)},
+                new[] {"concat", "--help"},
+                new[]
+                {
+                    "Usage",
+                    TestAppName, "concat", "-i", "<values...>", "[options]",
+                }
             );
         }
 
-        [Test]
         [TestCaseSource(nameof(GetTestCases_RunAsync))]
-        public async Task RunAsync_Test(IReadOnlyList<Type> commandTypes, IReadOnlyList<string> commandLineArguments, string expectedStdOut)
+        public async Task RunAsync_Test(
+            IReadOnlyList<Type> commandTypes,
+            IReadOnlyList<string> commandLineArguments,
+            IReadOnlyDictionary<string, string> environmentVariables,
+            string? expectedStdOut = null)
         {
             // Arrange
-            using (var stdout = new StringWriter())
-            {
-                var console = new VirtualConsole(stdout);
+            await using var stdOutStream = new StringWriter();
+            var console = new VirtualConsole(stdOutStream);
 
             var application = new CliApplicationBuilder()
                 .AddCommands(commandTypes)
+                .UseTitle(TestAppName)
+                .UseExecutableName(TestAppName)
+                .UseVersionText(TestVersionText)
                 .UseConsole(console)
                 .Build();
 
             // Act
-                var exitCode = await application.RunAsync(commandLineArguments);
+            var exitCode = await application.RunAsync(commandLineArguments, environmentVariables);
+            var stdOut = stdOutStream.ToString().Trim();
 
             // Assert
             exitCode.Should().Be(0);
-                stdout.ToString().Trim().Should().Be(expectedStdOut);
-            }
+            stdOut.Should().NotBeNullOrWhiteSpace();
+
+            if (expectedStdOut != null)
+                stdOut.Should().Be(expectedStdOut);
+
+            Console.WriteLine(stdOut);
         }
 
-        [Test]
-        [TestCaseSource(nameof(GetTestCases_HelpAndVersion_RunAsync))]
-        public async Task RunAsync_HelpAndVersion_Test(IReadOnlyList<Type> commandTypes, IReadOnlyList<string> commandLineArguments)
-        {
-            // Arrange
-            using (var stdout = new StringWriter())
-            {
-                var console = new VirtualConsole(stdout);
-
-                var application = new CliApplicationBuilder()
-                    .AddCommands(commandTypes)
-                    .UseConsole(console)
-                    .Build();
-
-                // Act
-                var exitCode = await application.RunAsync(commandLineArguments);
-
-                // Assert
-                exitCode.Should().Be(0);
-                stdout.ToString().Should().NotBeNullOrWhiteSpace();
-            }
-        }
-
-        [Test]
         [TestCaseSource(nameof(GetTestCases_RunAsync_Negative))]
-        public async Task RunAsync_Negative_Test(IReadOnlyList<Type> commandTypes, IReadOnlyList<string> commandLineArguments)
+        public async Task RunAsync_Negative_Test(
+            IReadOnlyList<Type> commandTypes,
+            IReadOnlyList<string> commandLineArguments,
+            IReadOnlyDictionary<string, string> environmentVariables,
+            string? expectedStdErr = null,
+            int? expectedExitCode = null)
         {
             // Arrange
-            using (var stderr = new StringWriter())
-            {
-                var console = new VirtualConsole(TextWriter.Null, stderr);
+            await using var stdErrStream = new StringWriter();
+            var console = new VirtualConsole(TextWriter.Null, stdErrStream);
 
             var application = new CliApplicationBuilder()
                 .AddCommands(commandTypes)
+                .UseTitle(TestAppName)
+                .UseExecutableName(TestAppName)
+                .UseVersionText(TestVersionText)
                 .UseConsole(console)
                 .Build();
 
             // Act
-                var exitCode = await application.RunAsync(commandLineArguments);
+            var exitCode = await application.RunAsync(commandLineArguments, environmentVariables);
+            var stderr = stdErrStream.ToString().Trim();
 
             // Assert
             exitCode.Should().NotBe(0);
-                stderr.ToString().Should().NotBeNullOrWhiteSpace();
-            }
+            stderr.Should().NotBeNullOrWhiteSpace();
+
+            if (expectedExitCode != null)
+                exitCode.Should().Be(expectedExitCode);
+
+            if (expectedStdErr != null)
+                stderr.Should().Be(expectedStdErr);
+
+            Console.WriteLine(stderr);
+        }
+
+        [TestCaseSource(nameof(GetTestCases_RunAsync_Help))]
+        public async Task RunAsync_Help_Test(
+            IReadOnlyList<Type> commandTypes,
+            IReadOnlyList<string> commandLineArguments,
+            IReadOnlyList<string>? expectedSubstrings = null)
+        {
+            // Arrange
+            await using var stdOutStream = new StringWriter();
+            var console = new VirtualConsole(stdOutStream);
+
+            var application = new CliApplicationBuilder()
+                .AddCommands(commandTypes)
+                .UseTitle(TestAppName)
+                .UseExecutableName(TestAppName)
+                .UseVersionText(TestVersionText)
+                .UseConsole(console)
+                .Build();
+
+            var environmentVariables = new Dictionary<string, string>();
+
+            // Act
+            var exitCode = await application.RunAsync(commandLineArguments, environmentVariables);
+            var stdOut = stdOutStream.ToString().Trim();
+
+            // Assert
+            exitCode.Should().Be(0);
+            stdOut.Should().NotBeNullOrWhiteSpace();
+
+            if (expectedSubstrings != null)
+                stdOut.Should().ContainAll(expectedSubstrings);
+
+            Console.WriteLine(stdOut);
+        }
+
+        [Test]
+        public async Task RunAsync_Cancellation_Test()
+        {
+            // Arrange
+            using var cancellationTokenSource = new CancellationTokenSource();
+
+            await using var stdOutStream = new StringWriter();
+            await using var stdErrStream = new StringWriter();
+            var console = new VirtualConsole(stdOutStream, stdErrStream, cancellationTokenSource.Token);
+
+            var application = new CliApplicationBuilder()
+                .AddCommand(typeof(CancellableCommand))
+                .UseConsole(console)
+                .Build();
+
+            var commandLineArguments = new[] {"cancel"};
+            var environmentVariables = new Dictionary<string, string>();
+
+            // Act
+            cancellationTokenSource.CancelAfter(TimeSpan.FromSeconds(0.2));
+            var exitCode = await application.RunAsync(commandLineArguments, environmentVariables);
+            var stdOut = stdOutStream.ToString().Trim();
+            var stdErr = stdErrStream.ToString().Trim();
+
+            // Assert
+            exitCode.Should().NotBe(0);
+            stdOut.Should().BeNullOrWhiteSpace();
+            stdErr.Should().NotBeNullOrWhiteSpace();
+
+            Console.WriteLine(stdErr);
         }
     }
 }

CliFx.Tests/CliFx.Tests.csproj

@@ -1,25 +1,22 @@
 <Project Sdk="Microsoft.NET.Sdk">
+  <Import Project="../CliFx.props" />
 
   <PropertyGroup>
-    <TargetFramework>net46</TargetFramework>
+    <TargetFramework>netcoreapp3.1</TargetFramework>
     <IsPackable>false</IsPackable>
     <IsTestProject>true</IsTestProject>
     <CollectCoverage>true</CollectCoverage>
     <CoverletOutputFormat>opencover</CoverletOutputFormat>
     <CoverletOutput>bin/$(Configuration)/Coverage.xml</CoverletOutput>
-    <LangVersion>latest</LangVersion>
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="FluentAssertions" Version="5.8.0" />
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.2.0" />
+    <PackageReference Include="CliWrap" Version="2.5.0" />
+    <PackageReference Include="FluentAssertions" Version="5.10.0" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.4.0" />
     <PackageReference Include="NUnit" Version="3.12.0" />
-    <PackageReference Include="NUnit3TestAdapter" Version="3.14.0" />
-    <PackageReference Include="CliWrap" Version="2.3.1" />
-    <PackageReference Include="coverlet.msbuild" Version="2.6.3">
-      <PrivateAssets>all</PrivateAssets>
-      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
-    </PackageReference>
+    <PackageReference Include="NUnit3TestAdapter" Version="3.16.1" />
+    <PackageReference Include="coverlet.msbuild" Version="2.8.0" PrivateAssets="all" />
   </ItemGroup>
 
   <ItemGroup>
@@ -27,4 +24,8 @@
     <ProjectReference Include="..\CliFx\CliFx.csproj" />
   </ItemGroup>
 
+  <Target Name="Copy dummy's runtime config" AfterTargets="AfterBuild">
+    <Copy SourceFiles="../CliFx.Tests.Dummy/bin/$(Configuration)/$(TargetFramework)/CliFx.Tests.Dummy.runtimeconfig.json" DestinationFiles="$(OutputPath)CliFx.Tests.Dummy.runtimeconfig.json" />
+  </Target>
+
 </Project>

CliFx.Tests/CommandFactoryTests.Commands.cs

@@ -1,15 +0,0 @@
-using System.Threading.Tasks;
-using CliFx.Attributes;
-using CliFx.Services;
-
-namespace CliFx.Tests
-{
-    public partial class CommandFactoryTests
-    {
-        [Command]
-        private class TestCommand : ICommand
-        {
-            public Task ExecuteAsync(IConsole console) => Task.CompletedTask;
-        }
-    }
-}

CliFx.Tests/CommandFactoryTests.cs

@@ -1,36 +0,0 @@
-using System;
-using System.Collections.Generic;
-using System.Linq;
-using CliFx.Models;
-using CliFx.Services;
-using FluentAssertions;
-using NUnit.Framework;
-
-namespace CliFx.Tests
-{
-    [TestFixture]
-    public partial class CommandFactoryTests
-    {
-        private static CommandSchema GetCommandSchema(Type commandType) =>
-            new CommandSchemaResolver().GetCommandSchemas(new[] {commandType}).Single();
-
-        private static IEnumerable<TestCaseData> GetTestCases_CreateCommand()
-        {
-            yield return new TestCaseData(GetCommandSchema(typeof(TestCommand)));
-        }
-
-        [Test]
-        [TestCaseSource(nameof(GetTestCases_CreateCommand))]
-        public void CreateCommand_Test(CommandSchema commandSchema)
-        {
-            // Arrange
-            var factory = new CommandFactory();
-
-            // Act
-            var command = factory.CreateCommand(commandSchema);
-
-            // Assert
-            command.Should().BeOfType(commandSchema.Type);
-        }
-    }
-}

CliFx.Tests/CommandInitializerTests.Commands.cs

@@ -1,21 +0,0 @@
-using System.Threading.Tasks;
-using CliFx.Attributes;
-using CliFx.Services;
-
-namespace CliFx.Tests
-{
-    public partial class CommandInitializerTests
-    {
-        [Command]
-        private class TestCommand : ICommand
-        {
-            [CommandOption("int", 'i', IsRequired = true)]
-            public int IntOption { get; set; } = 24;
-
-            [CommandOption("str", 's')]
-            public string StringOption { get; set; } = "foo bar";
-
-            public Task ExecuteAsync(IConsole console) => Task.CompletedTask;
-        }
-    }
-}

CliFx.Tests/CommandInitializerTests.cs

@@ -1,96 +0,0 @@
-using System;
-using System.Collections.Generic;
-using System.Linq;
-using CliFx.Exceptions;
-using CliFx.Models;
-using CliFx.Services;
-using FluentAssertions;
-using NUnit.Framework;
-
-namespace CliFx.Tests
-{
-    [TestFixture]
-    public partial class CommandInitializerTests
-    {
-        private static CommandSchema GetCommandSchema(Type commandType) =>
-            new CommandSchemaResolver().GetCommandSchemas(new[] {commandType}).Single();
-
-        private static IEnumerable<TestCaseData> GetTestCases_InitializeCommand()
-        {
-            yield return new TestCaseData(
-                new TestCommand(),
-                GetCommandSchema(typeof(TestCommand)),
-                new CommandInput(new[]
-                {
-                    new CommandOptionInput("int", "13")
-                }),
-                new TestCommand {IntOption = 13}
-            );
-
-            yield return new TestCaseData(
-                new TestCommand(),
-                GetCommandSchema(typeof(TestCommand)),
-                new CommandInput(new[]
-                {
-                    new CommandOptionInput("int", "13"),
-                    new CommandOptionInput("str", "hello world")
-                }),
-                new TestCommand {IntOption = 13, StringOption = "hello world"}
-            );
-
-            yield return new TestCaseData(
-                new TestCommand(),
-                GetCommandSchema(typeof(TestCommand)),
-                new CommandInput(new[]
-                {
-                    new CommandOptionInput("i", "13")
-                }),
-                new TestCommand {IntOption = 13}
-            );
-        }
-
-        private static IEnumerable<TestCaseData> GetTestCases_InitializeCommand_Negative()
-        {
-            yield return new TestCaseData(
-                new TestCommand(),
-                GetCommandSchema(typeof(TestCommand)),
-                CommandInput.Empty
-            );
-
-            yield return new TestCaseData(
-                new TestCommand(),
-                GetCommandSchema(typeof(TestCommand)),
-                new CommandInput(new[]
-                {
-                    new CommandOptionInput("str", "hello world")
-                })
-            );
-        }
-
-        [Test]
-        [TestCaseSource(nameof(GetTestCases_InitializeCommand))]
-        public void InitializeCommand_Test(ICommand command, CommandSchema commandSchema, CommandInput commandInput, ICommand expectedCommand)
-        {
-            // Arrange
-            var initializer = new CommandInitializer();
-
-            // Act
-            initializer.InitializeCommand(command, commandSchema, commandInput);
-
-            // Assert
-            command.Should().BeEquivalentTo(expectedCommand, o => o.RespectingRuntimeTypes());
-        }
-
-        [Test]
-        [TestCaseSource(nameof(GetTestCases_InitializeCommand_Negative))]
-        public void InitializeCommand_Negative_Test(ICommand command, CommandSchema commandSchema, CommandInput commandInput)
-        {
-            // Arrange
-            var initializer = new CommandInitializer();
-
-            // Act & Assert
-            initializer.Invoking(i => i.InitializeCommand(command, commandSchema, commandInput))
-                .Should().ThrowExactly<MissingCommandOptionInputException>();
-        }
-    }
-}

CliFx.Tests/CommandInputParserTests.cs

@@ -1,184 +0,0 @@
-using System.Collections.Generic;
-using CliFx.Models;
-using CliFx.Services;
-using FluentAssertions;
-using NUnit.Framework;
-
-namespace CliFx.Tests
-{
-    [TestFixture]
-    public class CommandInputParserTests
-    {
-        private static IEnumerable<TestCaseData> GetTestCases_ParseCommandInput()
-        {
-            yield return new TestCaseData(new string[0], CommandInput.Empty);
-
-            yield return new TestCaseData(
-                new[] {"--option", "value"},
-                new CommandInput(new[]
-                {
-                    new CommandOptionInput("option", "value")
-                })
-            );
-
-            yield return new TestCaseData(
-                new[] {"--option1", "value1", "--option2", "value2"},
-                new CommandInput(new[]
-                {
-                    new CommandOptionInput("option1", "value1"),
-                    new CommandOptionInput("option2", "value2")
-                })
-            );
-
-            yield return new TestCaseData(
-                new[] {"--option", "value1", "value2"},
-                new CommandInput(new[]
-                {
-                    new CommandOptionInput("option", new[] {"value1", "value2"})
-                })
-            );
-
-            yield return new TestCaseData(
-                new[] {"--option", "value1", "--option", "value2"},
-                new CommandInput(new[]
-                {
-                    new CommandOptionInput("option", new[] {"value1", "value2"})
-                })
-            );
-
-            yield return new TestCaseData(
-                new[] {"-a", "value"},
-                new CommandInput(new[]
-                {
-                    new CommandOptionInput("a", "value")
-                })
-            );
-
-            yield return new TestCaseData(
-                new[] {"-a", "value1", "-b", "value2"},
-                new CommandInput(new[]
-                {
-                    new CommandOptionInput("a", "value1"),
-                    new CommandOptionInput("b", "value2")
-                })
-            );
-
-            yield return new TestCaseData(
-                new[] {"-a", "value1", "value2"},
-                new CommandInput(new[]
-                {
-                    new CommandOptionInput("a", new[] {"value1", "value2"})
-                })
-            );
-
-            yield return new TestCaseData(
-                new[] {"-a", "value1", "-a", "value2"},
-                new CommandInput(new[]
-                {
-                    new CommandOptionInput("a", new[] {"value1", "value2"})
-                })
-            );
-
-            yield return new TestCaseData(
-                new[] {"--option1", "value1", "-b", "value2"},
-                new CommandInput(new[]
-                {
-                    new CommandOptionInput("option1", "value1"),
-                    new CommandOptionInput("b", "value2")
-                })
-            );
-
-            yield return new TestCaseData(
-                new[] {"--switch"},
-                new CommandInput(new[]
-                {
-                    new CommandOptionInput("switch")
-                })
-            );
-
-            yield return new TestCaseData(
-                new[] {"--switch1", "--switch2"},
-                new CommandInput(new[]
-                {
-                    new CommandOptionInput("switch1"),
-                    new CommandOptionInput("switch2")
-                })
-            );
-
-            yield return new TestCaseData(
-                new[] {"-s"},
-                new CommandInput(new[]
-                {
-                    new CommandOptionInput("s")
-                })
-            );
-
-            yield return new TestCaseData(
-                new[] {"-a", "-b"},
-                new CommandInput(new[]
-                {
-                    new CommandOptionInput("a"),
-                    new CommandOptionInput("b")
-                })
-            );
-
-            yield return new TestCaseData(
-                new[] {"-ab"},
-                new CommandInput(new[]
-                {
-                    new CommandOptionInput("a"),
-                    new CommandOptionInput("b")
-                })
-            );
-
-            yield return new TestCaseData(
-                new[] {"-ab", "value"},
-                new CommandInput(new[]
-                {
-                    new CommandOptionInput("a"),
-                    new CommandOptionInput("b", "value")
-                })
-            );
-
-            yield return new TestCaseData(
-                new[] {"command"},
-                new CommandInput("command")
-            );
-
-            yield return new TestCaseData(
-                new[] {"command", "--option", "value"},
-                new CommandInput("command", new[]
-                {
-                    new CommandOptionInput("option", "value")
-                })
-            );
-
-            yield return new TestCaseData(
-                new[] {"long", "command", "name"},
-                new CommandInput("long command name")
-            );
-
-            yield return new TestCaseData(
-                new[] {"long", "command", "name", "--option", "value"},
-                new CommandInput("long command name", new[]
-                {
-                    new CommandOptionInput("option", "value")
-                })
-            );
-        }
-
-        [Test]
-        [TestCaseSource(nameof(GetTestCases_ParseCommandInput))]
-        public void ParseCommandInput_Test(IReadOnlyList<string> commandLineArguments, CommandInput expectedCommandInput)
-        {
-            // Arrange
-            var parser = new CommandInputParser();
-
-            // Act
-            var commandInput = parser.ParseCommandInput(commandLineArguments);
-
-            // Assert
-            commandInput.Should().BeEquivalentTo(expectedCommandInput);
-        }
-    }
-}

CliFx.Tests/CommandOptionInputConverterTests.Types.cs

@@ -1,63 +0,0 @@
-using System;
-
-namespace CliFx.Tests
-{
-    public partial class CommandOptionInputConverterTests
-    {
-        private enum TestEnum
-        {
-            Value1,
-            Value2,
-            Value3
-        }
-
-        private class TestStringConstructable
-        {
-            public string Value { get; }
-
-            public TestStringConstructable(string value)
-            {
-                Value = value;
-            }
-        }
-
-        private class TestStringParseable
-        {
-            public string Value { get; }
-
-            private TestStringParseable(string value)
-            {
-                Value = value;
-            }
-
-            public static TestStringParseable Parse(string value) => new TestStringParseable(value);
-        }
-
-        private class TestStringParseableWithFormatProvider
-        {
-            public string Value { get; }
-
-            private TestStringParseableWithFormatProvider(string value)
-            {
-                Value = value;
-            }
-
-            public static TestStringParseableWithFormatProvider Parse(string value, IFormatProvider formatProvider) =>
-                new TestStringParseableWithFormatProvider(value + " " + formatProvider);
-        }
-    }
-
-    // Negative
-    public partial class CommandOptionInputConverterTests
-    {
-        private class NonStringParseable
-        {
-            public int Value { get; }
-
-            public NonStringParseable(int value)
-            {
-                Value = value;
-            }
-        }
-    }
-}

CliFx.Tests/CommandOptionInputConverterTests.cs

@@ -1,305 +0,0 @@
-using System;
-using System.Collections;
-using System.Collections.Generic;
-using System.Globalization;
-using CliFx.Exceptions;
-using CliFx.Models;
-using CliFx.Services;
-using FluentAssertions;
-using NUnit.Framework;
-
-namespace CliFx.Tests
-{
-    [TestFixture]
-    public partial class CommandOptionInputConverterTests
-    {
-        private static IEnumerable<TestCaseData> GetTestCases_ConvertOptionInput()
-        {
-            yield return new TestCaseData(
-                new CommandOptionInput("option", "value"),
-                typeof(string),
-                "value"
-            );
-
-            yield return new TestCaseData(
-                new CommandOptionInput("option", "value"),
-                typeof(object),
-                "value"
-            );
-
-            yield return new TestCaseData(
-                new CommandOptionInput("option", "true"),
-                typeof(bool),
-                true
-            );
-
-            yield return new TestCaseData(
-                new CommandOptionInput("option", "false"),
-                typeof(bool),
-                false
-            );
-
-            yield return new TestCaseData(
-                new CommandOptionInput("option"),
-                typeof(bool),
-                true
-            );
-
-            yield return new TestCaseData(
-                new CommandOptionInput("option", "a"),
-                typeof(char),
-                'a'
-            );
-
-            yield return new TestCaseData(
-                new CommandOptionInput("option", "15"),
-                typeof(sbyte),
-                (sbyte) 15
-            );
-
-            yield return new TestCaseData(
-                new CommandOptionInput("option", "15"),
-                typeof(byte),
-                (byte) 15
-            );
-
-            yield return new TestCaseData(
-                new CommandOptionInput("option", "15"),
-                typeof(short),
-                (short) 15
-            );
-
-            yield return new TestCaseData(
-                new CommandOptionInput("option", "15"),
-                typeof(ushort),
-                (ushort) 15
-            );
-
-            yield return new TestCaseData(
-                new CommandOptionInput("option", "123"),
-                typeof(int),
-                123
-            );
-
-            yield return new TestCaseData(
-                new CommandOptionInput("option", "123"),
-                typeof(uint),
-                123u
-            );
-
-            yield return new TestCaseData(
-                new CommandOptionInput("option", "123"),
-                typeof(long),
-                123L
-            );
-
-            yield return new TestCaseData(
-                new CommandOptionInput("option", "123"),
-                typeof(ulong),
-                123UL
-            );
-
-            yield return new TestCaseData(
-                new CommandOptionInput("option", "123.45"),
-                typeof(float),
-                123.45f
-            );
-
-            yield return new TestCaseData(
-                new CommandOptionInput("option", "123.45"),
-                typeof(double),
-                123.45
-            );
-
-            yield return new TestCaseData(
-                new CommandOptionInput("option", "123.45"),
-                typeof(decimal),
-                123.45m
-            );
-
-            yield return new TestCaseData(
-                new CommandOptionInput("option", "28 Apr 1995"),
-                typeof(DateTime),
-                new DateTime(1995, 04, 28)
-            );
-
-            yield return new TestCaseData(
-                new CommandOptionInput("option", "28 Apr 1995"),
-                typeof(DateTimeOffset),
-                new DateTimeOffset(new DateTime(1995, 04, 28))
-            );
-
-            yield return new TestCaseData(
-                new CommandOptionInput("option", "00:14:59"),
-                typeof(TimeSpan),
-                new TimeSpan(00, 14, 59)
-            );
-
-            yield return new TestCaseData(
-                new CommandOptionInput("option", "value2"),
-                typeof(TestEnum),
-                TestEnum.Value2
-            );
-
-            yield return new TestCaseData(
-                new CommandOptionInput("option", "666"),
-                typeof(int?),
-                666
-            );
-
-            yield return new TestCaseData(
-                new CommandOptionInput("option"),
-                typeof(int?),
-                null
-            );
-
-            yield return new TestCaseData(
-                new CommandOptionInput("option", "value3"),
-                typeof(TestEnum?),
-                TestEnum.Value3
-            );
-
-            yield return new TestCaseData(
-                new CommandOptionInput("option"),
-                typeof(TestEnum?),
-                null
-            );
-
-            yield return new TestCaseData(
-                new CommandOptionInput("option", "01:00:00"),
-                typeof(TimeSpan?),
-                new TimeSpan(01, 00, 00)
-            );
-
-            yield return new TestCaseData(
-                new CommandOptionInput("option"),
-                typeof(TimeSpan?),
-                null
-            );
-
-            yield return new TestCaseData(
-                new CommandOptionInput("option", "value"),
-                typeof(TestStringConstructable),
-                new TestStringConstructable("value")
-            );
-
-            yield return new TestCaseData(
-                new CommandOptionInput("option", "value"),
-                typeof(TestStringParseable),
-                TestStringParseable.Parse("value")
-            );
-
-            yield return new TestCaseData(
-                new CommandOptionInput("option", "value"),
-                typeof(TestStringParseableWithFormatProvider),
-                TestStringParseableWithFormatProvider.Parse("value", CultureInfo.InvariantCulture)
-            );
-
-            yield return new TestCaseData(
-                new CommandOptionInput("option", new[] {"value1", "value2"}),
-                typeof(string[]),
-                new[] {"value1", "value2"}
-            );
-
-            yield return new TestCaseData(
-                new CommandOptionInput("option", new[] {"value1", "value2"}),
-                typeof(object[]),
-                new[] {"value1", "value2"}
-            );
-
-            yield return new TestCaseData(
-                new CommandOptionInput("option", new[] {"47", "69"}),
-                typeof(int[]),
-                new[] {47, 69}
-            );
-
-            yield return new TestCaseData(
-                new CommandOptionInput("option", new[] {"value1", "value3"}),
-                typeof(TestEnum[]),
-                new[] {TestEnum.Value1, TestEnum.Value3}
-            );
-
-            yield return new TestCaseData(
-                new CommandOptionInput("option", new[] {"1337", "2441"}),
-                typeof(int?[]),
-                new int?[] {1337, 2441}
-            );
-
-            yield return new TestCaseData(
-                new CommandOptionInput("option", new[] {"value1", "value2"}),
-                typeof(TestStringConstructable[]),
-                new[] {new TestStringConstructable("value1"), new TestStringConstructable("value2")}
-            );
-
-            yield return new TestCaseData(
-                new CommandOptionInput("option", new[] {"value1", "value2"}),
-                typeof(IEnumerable),
-                new[] {"value1", "value2"}
-            );
-
-            yield return new TestCaseData(
-                new CommandOptionInput("option", new[] {"value1", "value2"}),
-                typeof(IEnumerable<string>),
-                new[] {"value1", "value2"}
-            );
-
-            yield return new TestCaseData(
-                new CommandOptionInput("option", new[] {"value1", "value2"}),
-                typeof(IReadOnlyList<string>),
-                new[] {"value1", "value2"}
-            );
-
-            yield return new TestCaseData(
-                new CommandOptionInput("option", new[] {"value1", "value2"}),
-                typeof(List<string>),
-                new List<string> {"value1", "value2"}
-            );
-
-            yield return new TestCaseData(
-                new CommandOptionInput("option", new[] {"value1", "value2"}),
-                typeof(HashSet<string>),
-                new HashSet<string> {"value1", "value2"}
-            );
-        }
-
-        private static IEnumerable<TestCaseData> GetTestCases_ConvertOptionInput_Negative()
-        {
-            yield return new TestCaseData(
-                new CommandOptionInput("option", "1234.5"),
-                typeof(int)
-            );
-
-            yield return new TestCaseData(
-                new CommandOptionInput("option", "123"),
-                typeof(NonStringParseable)
-            );
-        }
-
-        [Test]
-        [TestCaseSource(nameof(GetTestCases_ConvertOptionInput))]
-        public void ConvertOptionInput_Test(CommandOptionInput optionInput, Type targetType, object expectedConvertedValue)
-        {
-            // Arrange
-            var converter = new CommandOptionInputConverter();
-
-            // Act
-            var convertedValue = converter.ConvertOptionInput(optionInput, targetType);
-
-            // Assert
-            convertedValue.Should().BeEquivalentTo(expectedConvertedValue);
-            convertedValue?.Should().BeAssignableTo(targetType);
-        }
-
-        [Test]
-        [TestCaseSource(nameof(GetTestCases_ConvertOptionInput_Negative))]
-        public void ConvertOptionInput_Negative_Test(CommandOptionInput optionInput, Type targetType)
-        {
-            // Arrange
-            var converter = new CommandOptionInputConverter();
-
-            // Act & Assert
-            converter.Invoking(c => c.ConvertOptionInput(optionInput, targetType))
-                .Should().ThrowExactly<InvalidCommandOptionInputException>();
-        }
-    }
-}

CliFx.Tests/CommandSchemaResolverTests.Commands.cs

@@ -1,81 +0,0 @@
-using System;
-using System.Threading.Tasks;
-using CliFx.Attributes;
-using CliFx.Services;
-
-namespace CliFx.Tests
-{
-    public partial class CommandSchemaResolverTests
-    {
-        [Command("cmd", Description = "NormalCommand1 description.")]
-        private class NormalCommand1 : ICommand
-        {
-            [CommandOption("option-a", 'a')]
-            public int OptionA { get; set; }
-
-            [CommandOption("option-b", IsRequired = true)]
-            public string OptionB { get; set; }
-
-            public Task ExecuteAsync(IConsole console) => Task.CompletedTask;
-        }
-
-        [Command(Description = "NormalCommand2 description.")]
-        private class NormalCommand2 : ICommand
-        {
-            [CommandOption("option-c", Description = "OptionC description.")]
-            public bool OptionC { get; set; }
-
-            [CommandOption("option-d", 'd')]
-            public DateTimeOffset OptionD { get; set; }
-
-            public string NotAnOption { get; set; }
-
-            public Task ExecuteAsync(IConsole console) => Task.CompletedTask;
-        }
-    }
-
-    // Negative
-    public partial class CommandSchemaResolverTests
-    {
-        [Command("conflict")]
-        private class ConflictingCommand1 : ICommand
-        {
-            public Task ExecuteAsync(IConsole console) => Task.CompletedTask;
-        }
-
-        [Command("conflict")]
-        private class ConflictingCommand2 : ICommand
-        {
-            public Task ExecuteAsync(IConsole console) => Task.CompletedTask;
-        }
-
-        [Command]
-        private class InvalidCommand1
-        {
-        }
-
-        [Command]
-        private class InvalidCommand2 : ICommand
-        {
-            [CommandOption("conflict")]
-            public string ConflictingOption1 { get; set; }
-
-            [CommandOption("conflict")]
-            public string ConflictingOption2 { get; set; }
-
-            public Task ExecuteAsync(IConsole console) => Task.CompletedTask;
-        }
-
-        [Command]
-        private class InvalidCommand3 : ICommand
-        {
-            [CommandOption('c')]
-            public string ConflictingOption1 { get; set; }
-
-            [CommandOption('c')]
-            public string ConflictingOption2 { get; set; }
-
-            public Task ExecuteAsync(IConsole console) => Task.CompletedTask;
-        }
-    }
-}

CliFx.Tests/CommandSchemaResolverTests.cs

@@ -1,94 +0,0 @@
-using System;
-using System.Collections.Generic;
-using CliFx.Exceptions;
-using CliFx.Models;
-using CliFx.Services;
-using FluentAssertions;
-using NUnit.Framework;
-
-namespace CliFx.Tests
-{
-    [TestFixture]
-    public partial class CommandSchemaResolverTests
-    {
-        private static IEnumerable<TestCaseData> GetTestCases_GetCommandSchemas()
-        {
-            yield return new TestCaseData(
-                new[] {typeof(NormalCommand1), typeof(NormalCommand2)},
-                new[]
-                {
-                    new CommandSchema(typeof(NormalCommand1), "cmd", "NormalCommand1 description.",
-                        new[]
-                        {
-                            new CommandOptionSchema(typeof(NormalCommand1).GetProperty(nameof(NormalCommand1.OptionA)),
-                                "option-a", 'a', false, null),
-                            new CommandOptionSchema(typeof(NormalCommand1).GetProperty(nameof(NormalCommand1.OptionB)),
-                                "option-b", null, true, null)
-                        }),
-                    new CommandSchema(typeof(NormalCommand2), null, "NormalCommand2 description.",
-                        new[]
-                        {
-                            new CommandOptionSchema(typeof(NormalCommand2).GetProperty(nameof(NormalCommand2.OptionC)),
-                                "option-c", null, false, "OptionC description."),
-                            new CommandOptionSchema(typeof(NormalCommand2).GetProperty(nameof(NormalCommand2.OptionD)),
-                                "option-d", 'd', false, null)
-                        })
-                }
-            );
-        }
-
-        private static IEnumerable<TestCaseData> GetTestCases_GetCommandSchemas_Negative()
-        {
-            yield return new TestCaseData(new object[]
-            {
-                new Type[0]
-            });
-
-            yield return new TestCaseData(new object[]
-            {
-                new[] {typeof(ConflictingCommand1), typeof(ConflictingCommand2)}
-            });
-
-            yield return new TestCaseData(new object[]
-            {
-                new[] {typeof(InvalidCommand1)}
-            });
-
-            yield return new TestCaseData(new object[]
-            {
-                new[] {typeof(InvalidCommand2)}
-            });
-
-            yield return new TestCaseData(new object[]
-            {
-                new[] {typeof(InvalidCommand3)}
-            });
-        }
-
-        [Test]
-        [TestCaseSource(nameof(GetTestCases_GetCommandSchemas))]
-        public void GetCommandSchemas_Test(IReadOnlyList<Type> commandTypes, IReadOnlyList<CommandSchema> expectedCommandSchemas)
-        {
-            // Arrange
-            var commandSchemaResolver = new CommandSchemaResolver();
-
-            // Act
-            var commandSchemas = commandSchemaResolver.GetCommandSchemas(commandTypes);
-
-            // Assert
-            commandSchemas.Should().BeEquivalentTo(expectedCommandSchemas);
-        }
-
-        [Test]
-        [TestCaseSource(nameof(GetTestCases_GetCommandSchemas_Negative))]
-        public void GetCommandSchemas_Negative_Test(IReadOnlyList<Type> commandTypes)
-        {
-            // Arrange
-            var resolver = new CommandSchemaResolver();
-
-            // Act & Assert
-            resolver.Invoking(r => r.GetCommandSchemas(commandTypes))
-                .Should().ThrowExactly<InvalidCommandSchemaException>();
-        }
-    }
-}

CliFx.Tests/DefaultCommandFactoryTests.cs

@@ -0,0 +1,48 @@
+using System;
+using System.Collections.Generic;
+using CliFx.Exceptions;
+using CliFx.Tests.TestCommands;
+using CliFx.Tests.TestCustomTypes;
+using FluentAssertions;
+using NUnit.Framework;
+
+namespace CliFx.Tests
+{
+    [TestFixture]
+    public class DefaultCommandFactoryTests
+    {
+        private static IEnumerable<TestCaseData> GetTestCases_CreateInstance()
+        {
+            yield return new TestCaseData(typeof(HelloWorldDefaultCommand));
+        }
+
+        private static IEnumerable<TestCaseData> GetTestCases_CreateInstance_Negative()
+        {
+            yield return new TestCaseData(typeof(TestNonStringParseable));
+        }
+
+        [TestCaseSource(nameof(GetTestCases_CreateInstance))]
+        public void CreateInstance_Test(Type type)
+        {
+            // Arrange
+            var activator = new DefaultTypeActivator();
+
+            // Act
+            var obj = activator.CreateInstance(type);
+
+            // Assert
+            obj.Should().BeOfType(type);
+        }
+
+        [TestCaseSource(nameof(GetTestCases_CreateInstance_Negative))]
+        public void CreateInstance_Negative_Test(Type type)
+        {
+            // Arrange
+            var activator = new DefaultTypeActivator();
+
+            // Act & Assert
+            var ex = Assert.Throws<CliFxException>(() => activator.CreateInstance(type));
+            Console.WriteLine(ex.Message);
+        }
+    }
+}

CliFx.Tests/DelegateCommandFactoryTests.Commands.cs

@@ -1,15 +0,0 @@
-using System.Threading.Tasks;
-using CliFx.Attributes;
-using CliFx.Services;
-
-namespace CliFx.Tests
-{
-    public partial class DelegateCommandFactoryTests
-    {
-        [Command]
-        private class TestCommand : ICommand
-        {
-            public Task ExecuteAsync(IConsole console) => Task.CompletedTask;
-        }
-    }
-}

CliFx.Tests/DelegateCommandFactoryTests.cs

@@ -1,39 +1,53 @@
 using System;
 using System.Collections.Generic;
-using System.Linq;
-using CliFx.Models;
-using CliFx.Services;
+using CliFx.Exceptions;
+using CliFx.Tests.TestCommands;
 using FluentAssertions;
 using NUnit.Framework;
 
 namespace CliFx.Tests
 {
     [TestFixture]
-    public partial class DelegateCommandFactoryTests
+    public class DelegateCommandFactoryTests
     {
-        private static CommandSchema GetCommandSchema(Type commandType) =>
-            new CommandSchemaResolver().GetCommandSchemas(new[] {commandType}).Single();
-
-        private static IEnumerable<TestCaseData> GetTestCases_CreateCommand()
+        private static IEnumerable<TestCaseData> GetTestCases_CreateInstance()
         {
             yield return new TestCaseData(
-                new Func<CommandSchema, ICommand>(schema => (ICommand) Activator.CreateInstance(schema.Type)),
-                GetCommandSchema(typeof(TestCommand))
+                new Func<Type, object>(Activator.CreateInstance),
+                typeof(HelloWorldDefaultCommand)
             );
         }
 
-        [Test]
-        [TestCaseSource(nameof(GetTestCases_CreateCommand))]
-        public void CreateCommand_Test(Func<CommandSchema, ICommand> factoryMethod, CommandSchema commandSchema)
+        private static IEnumerable<TestCaseData> GetTestCases_CreateInstance_Negative()
+        {
+            yield return new TestCaseData(
+                new Func<Type, object>(_ => null),
+                typeof(HelloWorldDefaultCommand)
+            );
+        }
+
+        [TestCaseSource(nameof(GetTestCases_CreateInstance))]
+        public void CreateInstance_Test(Func<Type, object> activatorFunc, Type type)
         {
             // Arrange
-            var factory = new DelegateCommandFactory(factoryMethod);
+            var activator = new DelegateTypeActivator(activatorFunc);
 
             // Act
-            var command = factory.CreateCommand(commandSchema);
+            var obj = activator.CreateInstance(type);
 
             // Assert
-            command.Should().BeOfType(commandSchema.Type);
+            obj.Should().BeOfType(type);
+        }
+
+        [TestCaseSource(nameof(GetTestCases_CreateInstance_Negative))]
+        public void CreateInstance_Negative_Test(Func<Type, object> activatorFunc, Type type)
+        {
+            // Arrange
+            var activator = new DelegateTypeActivator(activatorFunc);
+
+            // Act & Assert
+            var ex = Assert.Throws<CliFxException>(() => activator.CreateInstance(type));
+            Console.WriteLine(ex.Message);
         }
     }
 }

CliFx.Tests/Domain/ApplicationSchemaTests.cs

@@ -0,0 +1,888 @@
+using System;
+using System.Collections.Generic;
+using System.Globalization;
+using System.IO;
+using CliFx.Domain;
+using CliFx.Exceptions;
+using CliFx.Tests.TestCommands;
+using CliFx.Tests.TestCustomTypes;
+using FluentAssertions;
+using NUnit.Framework;
+
+namespace CliFx.Tests.Domain
+{
+    [TestFixture]
+    internal partial class ApplicationSchemaTests
+    {
+        private static IEnumerable<TestCaseData> GetTestCases_Resolve()
+        {
+            yield return new TestCaseData(
+                new[]
+                {
+                    typeof(DivideCommand),
+                    typeof(ConcatCommand),
+                    typeof(EnvironmentVariableCommand)
+                },
+                new[]
+                {
+                    new CommandSchema(typeof(DivideCommand), "div", "Divide one number by another.",
+                        new CommandParameterSchema[0], new[]
+                        {
+                            new CommandOptionSchema(typeof(DivideCommand).GetProperty(nameof(DivideCommand.Dividend)),
+                                "dividend", 'D', null, true, "The number to divide."),
+                            new CommandOptionSchema(typeof(DivideCommand).GetProperty(nameof(DivideCommand.Divisor)),
+                                "divisor", 'd', null, true, "The number to divide by.")
+                        }),
+                    new CommandSchema(typeof(ConcatCommand), "concat", "Concatenate strings.",
+                        new CommandParameterSchema[0],
+                        new[]
+                        {
+                            new CommandOptionSchema(typeof(ConcatCommand).GetProperty(nameof(ConcatCommand.Inputs)),
+                                null, 'i', null, true, "Input strings."),
+                            new CommandOptionSchema(typeof(ConcatCommand).GetProperty(nameof(ConcatCommand.Separator)),
+                                null, 's', null, false, "String separator.")
+                        }),
+                    new CommandSchema(typeof(EnvironmentVariableCommand), null, "Reads option values from environment variables.",
+                        new CommandParameterSchema[0],
+                        new[]
+                        {
+                            new CommandOptionSchema(typeof(EnvironmentVariableCommand).GetProperty(nameof(EnvironmentVariableCommand.Option)),
+                                "opt", null, "ENV_SINGLE_VALUE", false, null)
+                        }
+                    )
+                }
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(SimpleParameterCommand)},
+                new[]
+                {
+                    new CommandSchema(typeof(SimpleParameterCommand), "param cmd2", "Command using positional parameters",
+                        new[]
+                        {
+                            new CommandParameterSchema(typeof(SimpleParameterCommand).GetProperty(nameof(SimpleParameterCommand.ParameterA)),
+                                0, "first", null),
+                            new CommandParameterSchema(typeof(SimpleParameterCommand).GetProperty(nameof(SimpleParameterCommand.ParameterB)),
+                                10, null, null)
+                        },
+                        new[]
+                        {
+                            new CommandOptionSchema(typeof(SimpleParameterCommand).GetProperty(nameof(SimpleParameterCommand.OptionA)),
+                                "option", 'o', null, false, null)
+                        })
+                }
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(HelloWorldDefaultCommand)},
+                new[]
+                {
+                    new CommandSchema(typeof(HelloWorldDefaultCommand), null, null,
+                        new CommandParameterSchema[0],
+                        new CommandOptionSchema[0])
+                }
+            );
+        }
+
+        private static IEnumerable<TestCaseData> GetTestCases_Resolve_Negative()
+        {
+            yield return new TestCaseData(new object[]
+            {
+                new Type[0]
+            });
+
+            // Command validation failure
+
+            yield return new TestCaseData(new object[]
+            {
+                new[] {typeof(NonImplementedCommand)}
+            });
+
+            yield return new TestCaseData(new object[]
+            {
+                // Same name
+                new[] {typeof(ExceptionCommand), typeof(CommandExceptionCommand)}
+            });
+
+            yield return new TestCaseData(new object[]
+            {
+                new[] {typeof(NonAnnotatedCommand)}
+            });
+
+            // Parameter validation failure
+
+            yield return new TestCaseData(new object[]
+            {
+                new[] {typeof(DuplicateParameterOrderCommand)}
+            });
+
+            yield return new TestCaseData(new object[]
+            {
+                new[] {typeof(DuplicateParameterNameCommand)}
+            });
+
+            yield return new TestCaseData(new object[]
+            {
+                new[] {typeof(MultipleNonScalarParametersCommand)}
+            });
+
+            yield return new TestCaseData(new object[]
+            {
+                new[] {typeof(NonLastNonScalarParameterCommand)}
+            });
+
+            // Option validation failure
+
+            yield return new TestCaseData(new object[]
+            {
+                new[] {typeof(DuplicateOptionNamesCommand)}
+            });
+
+            yield return new TestCaseData(new object[]
+            {
+                new[] {typeof(DuplicateOptionShortNamesCommand)}
+            });
+
+            yield return new TestCaseData(new object[]
+            {
+                new[] {typeof(DuplicateOptionEnvironmentVariableNamesCommand)}
+            });
+        }
+
+        [Test]
+        [TestCaseSource(nameof(GetTestCases_Resolve))]
+        public void Resolve_Test(
+            IReadOnlyList<Type> commandTypes,
+            IReadOnlyList<CommandSchema> expectedCommandSchemas)
+        {
+            // Act
+            var applicationSchema = ApplicationSchema.Resolve(commandTypes);
+
+            // Assert
+            applicationSchema.Commands.Should().BeEquivalentTo(expectedCommandSchemas);
+        }
+
+        [Test]
+        [TestCaseSource(nameof(GetTestCases_Resolve_Negative))]
+        public void Resolve_Negative_Test(IReadOnlyList<Type> commandTypes)
+        {
+            // Act & Assert
+            var ex = Assert.Throws<CliFxException>(() => ApplicationSchema.Resolve(commandTypes));
+            Console.WriteLine(ex.Message);
+        }
+    }
+
+    internal partial class ApplicationSchemaTests
+    {
+        private static IEnumerable<TestCaseData> GetTestCases_InitializeEntryPoint()
+        {
+            yield return new TestCaseData(
+                new[] {typeof(AllSupportedTypesCommand)},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput(nameof(AllSupportedTypesCommand.Object), "value")
+                    }),
+                new Dictionary<string, string>(),
+                new AllSupportedTypesCommand {Object = "value"}
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(AllSupportedTypesCommand)},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput(nameof(AllSupportedTypesCommand.String), "value")
+                    }),
+                new Dictionary<string, string>(),
+                new AllSupportedTypesCommand {String = "value"}
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(AllSupportedTypesCommand)},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput(nameof(AllSupportedTypesCommand.Bool), "true")
+                    }),
+                new Dictionary<string, string>(),
+                new AllSupportedTypesCommand {Bool = true}
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(AllSupportedTypesCommand)},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput(nameof(AllSupportedTypesCommand.Bool), "false")
+                    }),
+                new Dictionary<string, string>(),
+                new AllSupportedTypesCommand {Bool = false}
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(AllSupportedTypesCommand)},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput(nameof(AllSupportedTypesCommand.Bool))
+                    }),
+                new Dictionary<string, string>(),
+                new AllSupportedTypesCommand {Bool = true}
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(AllSupportedTypesCommand)},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput(nameof(AllSupportedTypesCommand.Char), "a")
+                    }),
+                new Dictionary<string, string>(),
+                new AllSupportedTypesCommand {Char = 'a'}
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(AllSupportedTypesCommand)},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput(nameof(AllSupportedTypesCommand.Sbyte), "15")
+                    }),
+                new Dictionary<string, string>(),
+                new AllSupportedTypesCommand {Sbyte = 15}
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(AllSupportedTypesCommand)},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput(nameof(AllSupportedTypesCommand.Byte), "15")
+                    }),
+                new Dictionary<string, string>(),
+                new AllSupportedTypesCommand {Byte = 15}
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(AllSupportedTypesCommand)},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput(nameof(AllSupportedTypesCommand.Short), "15")
+                    }),
+                new Dictionary<string, string>(),
+                new AllSupportedTypesCommand {Short = 15}
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(AllSupportedTypesCommand)},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput(nameof(AllSupportedTypesCommand.Ushort), "15")
+                    }),
+                new Dictionary<string, string>(),
+                new AllSupportedTypesCommand {Ushort = 15}
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(AllSupportedTypesCommand)},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput(nameof(AllSupportedTypesCommand.Int), "15")
+                    }),
+                new Dictionary<string, string>(),
+                new AllSupportedTypesCommand {Int = 15}
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(AllSupportedTypesCommand)},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput(nameof(AllSupportedTypesCommand.Uint), "15")
+                    }),
+                new Dictionary<string, string>(),
+                new AllSupportedTypesCommand {Uint = 15}
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(AllSupportedTypesCommand)},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput(nameof(AllSupportedTypesCommand.Long), "15")
+                    }),
+                new Dictionary<string, string>(),
+                new AllSupportedTypesCommand {Long = 15}
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(AllSupportedTypesCommand)},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput(nameof(AllSupportedTypesCommand.Ulong), "15")
+                    }),
+                new Dictionary<string, string>(),
+                new AllSupportedTypesCommand {Ulong = 15}
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(AllSupportedTypesCommand)},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput(nameof(AllSupportedTypesCommand.Float), "123.45")
+                    }),
+                new Dictionary<string, string>(),
+                new AllSupportedTypesCommand {Float = 123.45f}
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(AllSupportedTypesCommand)},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput(nameof(AllSupportedTypesCommand.Double), "123.45")
+                    }),
+                new Dictionary<string, string>(),
+                new AllSupportedTypesCommand {Double = 123.45}
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(AllSupportedTypesCommand)},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput(nameof(AllSupportedTypesCommand.Decimal), "123.45")
+                    }),
+                new Dictionary<string, string>(),
+                new AllSupportedTypesCommand {Decimal = 123.45m}
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(AllSupportedTypesCommand)},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput(nameof(AllSupportedTypesCommand.DateTime), "28 Apr 1995")
+                    }),
+                new Dictionary<string, string>(),
+                new AllSupportedTypesCommand {DateTime = new DateTime(1995, 04, 28)}
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(AllSupportedTypesCommand)},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput(nameof(AllSupportedTypesCommand.DateTimeOffset), "28 Apr 1995")
+                    }),
+                new Dictionary<string, string>(),
+                new AllSupportedTypesCommand {DateTimeOffset = new DateTime(1995, 04, 28)}
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(AllSupportedTypesCommand)},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput(nameof(AllSupportedTypesCommand.TimeSpan), "00:14:59")
+                    }),
+                new Dictionary<string, string>(),
+                new AllSupportedTypesCommand {TimeSpan = new TimeSpan(00, 14, 59)}
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(AllSupportedTypesCommand)},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput(nameof(AllSupportedTypesCommand.TestEnum), "value2")
+                    }),
+                new Dictionary<string, string>(),
+                new AllSupportedTypesCommand {TestEnum = TestEnum.Value2}
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(AllSupportedTypesCommand)},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput(nameof(AllSupportedTypesCommand.IntNullable), "666")
+                    }),
+                new Dictionary<string, string>(),
+                new AllSupportedTypesCommand {IntNullable = 666}
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(AllSupportedTypesCommand)},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput(nameof(AllSupportedTypesCommand.IntNullable))
+                    }),
+                new Dictionary<string, string>(),
+                new AllSupportedTypesCommand {IntNullable = null}
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(AllSupportedTypesCommand)},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput(nameof(AllSupportedTypesCommand.TestEnumNullable), "value3")
+                    }),
+                new Dictionary<string, string>(),
+                new AllSupportedTypesCommand {TestEnumNullable = TestEnum.Value3}
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(AllSupportedTypesCommand)},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput(nameof(AllSupportedTypesCommand.TestEnumNullable))
+                    }),
+                new Dictionary<string, string>(),
+                new AllSupportedTypesCommand {TestEnumNullable = null}
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(AllSupportedTypesCommand)},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput(nameof(AllSupportedTypesCommand.TimeSpanNullable), "01:00:00")
+                    }),
+                new Dictionary<string, string>(),
+                new AllSupportedTypesCommand {TimeSpanNullable = new TimeSpan(01, 00, 00)}
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(AllSupportedTypesCommand)},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput(nameof(AllSupportedTypesCommand.TimeSpanNullable))
+                    }),
+                new Dictionary<string, string>(),
+                new AllSupportedTypesCommand {TimeSpanNullable = null}
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(AllSupportedTypesCommand)},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput(nameof(AllSupportedTypesCommand.TestStringConstructable), "value")
+                    }),
+                new Dictionary<string, string>(),
+                new AllSupportedTypesCommand {TestStringConstructable = new TestStringConstructable("value")}
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(AllSupportedTypesCommand)},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput(nameof(AllSupportedTypesCommand.TestStringParseable), "value")
+                    }),
+                new Dictionary<string, string>(),
+                new AllSupportedTypesCommand {TestStringParseable = TestStringParseable.Parse("value")}
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(AllSupportedTypesCommand)},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput(nameof(AllSupportedTypesCommand.TestStringParseableWithFormatProvider), "value")
+                    }),
+                new Dictionary<string, string>(),
+                new AllSupportedTypesCommand
+                {
+                    TestStringParseableWithFormatProvider =
+                        TestStringParseableWithFormatProvider.Parse("value", CultureInfo.InvariantCulture)
+                }
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(AllSupportedTypesCommand)},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput(nameof(AllSupportedTypesCommand.ObjectArray), new[] {"value1", "value2"})
+                    }),
+                new Dictionary<string, string>(),
+                new AllSupportedTypesCommand {ObjectArray = new object[] {"value1", "value2"}}
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(AllSupportedTypesCommand)},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput(nameof(AllSupportedTypesCommand.StringArray), new[] {"value1", "value2"})
+                    }),
+                new Dictionary<string, string>(),
+                new AllSupportedTypesCommand {StringArray = new[] {"value1", "value2"}}
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(AllSupportedTypesCommand)},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput(nameof(AllSupportedTypesCommand.StringArray))
+                    }),
+                new Dictionary<string, string>(),
+                new AllSupportedTypesCommand {StringArray = new string[0]}
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(AllSupportedTypesCommand)},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput(nameof(AllSupportedTypesCommand.IntArray), new[] {"47", "69"})
+                    }),
+                new Dictionary<string, string>(),
+                new AllSupportedTypesCommand {IntArray = new[] {47, 69}}
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(AllSupportedTypesCommand)},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput(nameof(AllSupportedTypesCommand.TestEnumArray), new[] {"value1", "value3"})
+                    }),
+                new Dictionary<string, string>(),
+                new AllSupportedTypesCommand {TestEnumArray = new[] {TestEnum.Value1, TestEnum.Value3}}
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(AllSupportedTypesCommand)},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput(nameof(AllSupportedTypesCommand.IntNullableArray), new[] {"1337", "2441"})
+                    }),
+                new Dictionary<string, string>(),
+                new AllSupportedTypesCommand {IntNullableArray = new int?[] {1337, 2441}}
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(AllSupportedTypesCommand)},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput(nameof(AllSupportedTypesCommand.TestStringConstructableArray), new[] {"value1", "value2"})
+                    }),
+                new Dictionary<string, string>(),
+                new AllSupportedTypesCommand
+                {
+                    TestStringConstructableArray = new[]
+                    {
+                        new TestStringConstructable("value1"),
+                        new TestStringConstructable("value2")
+                    }
+                }
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(AllSupportedTypesCommand)},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput(nameof(AllSupportedTypesCommand.Enumerable), new[] {"value1", "value3"})
+                    }),
+                new Dictionary<string, string>(),
+                new AllSupportedTypesCommand {Enumerable = new[] {"value1", "value3"}}
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(AllSupportedTypesCommand)},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput(nameof(AllSupportedTypesCommand.StringEnumerable), new[] {"value1", "value3"})
+                    }),
+                new Dictionary<string, string>(),
+                new AllSupportedTypesCommand {StringEnumerable = new[] {"value1", "value3"}}
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(AllSupportedTypesCommand)},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput(nameof(AllSupportedTypesCommand.StringReadOnlyList), new[] {"value1", "value3"})
+                    }),
+                new Dictionary<string, string>(),
+                new AllSupportedTypesCommand {StringReadOnlyList = new[] {"value1", "value3"}}
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(AllSupportedTypesCommand)},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput(nameof(AllSupportedTypesCommand.StringList), new[] {"value1", "value3"})
+                    }),
+                new Dictionary<string, string>(),
+                new AllSupportedTypesCommand {StringList = new List<string> {"value1", "value3"}}
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(AllSupportedTypesCommand)},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput(nameof(AllSupportedTypesCommand.StringHashSet), new[] {"value1", "value3"})
+                    }),
+                new Dictionary<string, string>(),
+                new AllSupportedTypesCommand {StringHashSet = new HashSet<string> {"value1", "value3"}}
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(DivideCommand)},
+                new CommandLineInput(
+                    new[] {"div"},
+                    new[]
+                    {
+                        new CommandOptionInput("dividend", "13"),
+                        new CommandOptionInput("divisor", "8"),
+                    }),
+                new Dictionary<string, string>(),
+                new DivideCommand {Dividend = 13, Divisor = 8}
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(DivideCommand)},
+                new CommandLineInput(
+                    new[] {"div"},
+                    new[]
+                    {
+                        new CommandOptionInput("D", "13"),
+                        new CommandOptionInput("d", "8"),
+                    }),
+                new Dictionary<string, string>(),
+                new DivideCommand {Dividend = 13, Divisor = 8}
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(DivideCommand)},
+                new CommandLineInput(
+                    new[] {"div"},
+                    new[]
+                    {
+                        new CommandOptionInput("dividend", "13"),
+                        new CommandOptionInput("d", "8"),
+                    }),
+                new Dictionary<string, string>(),
+                new DivideCommand {Dividend = 13, Divisor = 8}
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(ConcatCommand)},
+                new CommandLineInput(
+                    new[] {"concat"},
+                    new[] {new CommandOptionInput("i", new[] {"foo", " ", "bar"}),}),
+                new Dictionary<string, string>(),
+                new ConcatCommand {Inputs = new[] {"foo", " ", "bar"}}
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(ConcatCommand)},
+                new CommandLineInput(
+                    new[] {"concat"},
+                    new[]
+                    {
+                        new CommandOptionInput("i", new[] {"foo", "bar"}),
+                        new CommandOptionInput("s", " "),
+                    }),
+                new Dictionary<string, string>(),
+                new ConcatCommand {Inputs = new[] {"foo", "bar"}, Separator = " "}
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(EnvironmentVariableCommand)},
+                CommandLineInput.Empty,
+                new Dictionary<string, string>
+                {
+                    ["ENV_SINGLE_VALUE"] = "A"
+                },
+                new EnvironmentVariableCommand {Option = "A"}
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(EnvironmentVariableWithMultipleValuesCommand)},
+                CommandLineInput.Empty,
+                new Dictionary<string, string>
+                {
+                    ["ENV_MULTIPLE_VALUES"] = string.Join(Path.PathSeparator, "A", "B", "C")
+                },
+                new EnvironmentVariableWithMultipleValuesCommand {Option = new[] {"A", "B", "C"}}
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(EnvironmentVariableCommand)},
+                new CommandLineInput(new[] {new CommandOptionInput("opt", "X")}),
+                new Dictionary<string, string>
+                {
+                    ["ENV_SINGLE_VALUE"] = "A"
+                },
+                new EnvironmentVariableCommand {Option = "X"}
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(EnvironmentVariableWithoutCollectionPropertyCommand)},
+                CommandLineInput.Empty,
+                new Dictionary<string, string>
+                {
+                    ["ENV_MULTIPLE_VALUES"] = string.Join(Path.PathSeparator, "A", "B", "C")
+                },
+                new EnvironmentVariableWithoutCollectionPropertyCommand {Option = string.Join(Path.PathSeparator, "A", "B", "C")}
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(ParameterCommand)},
+                new CommandLineInput(
+                    new[] {"param", "cmd", "abc", "123", "1", "2"},
+                    new[] {new CommandOptionInput("o", "option value")}),
+                new Dictionary<string, string>(),
+                new ParameterCommand
+                {
+                    ParameterA = "abc",
+                    ParameterB = 123,
+                    ParameterC = new[] {1, 2},
+                    OptionA = "option value"
+                }
+            );
+        }
+
+        private static IEnumerable<TestCaseData> GetTestCases_InitializeEntryPoint_Negative()
+        {
+            yield return new TestCaseData(
+                new[] {typeof(AllSupportedTypesCommand)},
+                new CommandLineInput(
+                    new[] {new CommandOptionInput(nameof(AllSupportedTypesCommand.Int), "1234.5")}),
+                new Dictionary<string, string>()
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(AllSupportedTypesCommand)},
+                new CommandLineInput(
+                    new[] {new CommandOptionInput(nameof(AllSupportedTypesCommand.Int), new[] {"123", "456"})}),
+                new Dictionary<string, string>()
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(AllSupportedTypesCommand)},
+                new CommandLineInput(
+                    new[] {new CommandOptionInput(nameof(AllSupportedTypesCommand.Int))}),
+                new Dictionary<string, string>()
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(AllSupportedTypesCommand)},
+                new CommandLineInput(
+                    new[] {new CommandOptionInput(nameof(AllSupportedTypesCommand.NonConvertible), "123")}),
+                new Dictionary<string, string>()
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(DivideCommand)},
+                new CommandLineInput(new[] {"div"}),
+                new Dictionary<string, string>()
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(DivideCommand)},
+                new CommandLineInput(new[] {"div", "-D", "13"}),
+                new Dictionary<string, string>()
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(ConcatCommand)},
+                new CommandLineInput(new[] {"concat"}),
+                new Dictionary<string, string>()
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(ConcatCommand)},
+                new CommandLineInput(
+                    new[] {"concat"},
+                    new[] {new CommandOptionInput("s", "_")}),
+                new Dictionary<string, string>()
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(ParameterCommand)},
+                new CommandLineInput(
+                    new[] {"param", "cmd"},
+                    new[] {new CommandOptionInput("o", "option value")}),
+                new Dictionary<string, string>()
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(ParameterCommand)},
+                new CommandLineInput(
+                    new[] {"param", "cmd", "abc", "123", "invalid"},
+                    new[] {new CommandOptionInput("o", "option value")}),
+                new Dictionary<string, string>()
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(DivideCommand)},
+                new CommandLineInput(new[] {"non-existing"}),
+                new Dictionary<string, string>()
+            );
+
+            yield return new TestCaseData(
+                new[] {typeof(BrokenEnumerableCommand)},
+                new CommandLineInput(new[] {"value1", "value2"}),
+                new Dictionary<string, string>()
+            );
+        }
+
+        [TestCaseSource(nameof(GetTestCases_InitializeEntryPoint))]
+        public void InitializeEntryPoint_Test(
+            IReadOnlyList<Type> commandTypes,
+            CommandLineInput commandLineInput,
+            IReadOnlyDictionary<string, string> environmentVariables,
+            ICommand expectedResult)
+        {
+            // Arrange
+            var applicationSchema = ApplicationSchema.Resolve(commandTypes);
+            var typeActivator = new DefaultTypeActivator();
+
+            // Act
+            var command = applicationSchema.InitializeEntryPoint(commandLineInput, environmentVariables, typeActivator);
+
+            // Assert
+            command.Should().BeEquivalentTo(expectedResult, o => o.RespectingRuntimeTypes());
+        }
+
+        [TestCaseSource(nameof(GetTestCases_InitializeEntryPoint_Negative))]
+        public void InitializeEntryPoint_Negative_Test(
+            IReadOnlyList<Type> commandTypes,
+            CommandLineInput commandLineInput,
+            IReadOnlyDictionary<string, string> environmentVariables)
+        {
+            // Arrange
+            var applicationSchema = ApplicationSchema.Resolve(commandTypes);
+            var typeActivator = new DefaultTypeActivator();
+
+            // Act & Assert
+            var ex = Assert.Throws<CliFxException>(() =>
+                applicationSchema.InitializeEntryPoint(commandLineInput, environmentVariables, typeActivator));
+            Console.WriteLine(ex.Message);
+        }
+    }
+}

CliFx.Tests/Domain/CommandLineInputTests.cs

@@ -0,0 +1,264 @@
+using System.Collections.Generic;
+using CliFx.Domain;
+using FluentAssertions;
+using NUnit.Framework;
+
+namespace CliFx.Tests.Domain
+{
+    [TestFixture]
+    internal class CommandLineInputTests
+    {
+        private static IEnumerable<TestCaseData> GetTestCases_Parse()
+        {
+            yield return new TestCaseData(
+                new string[0],
+                CommandLineInput.Empty
+            );
+
+            yield return new TestCaseData(
+                new[] {"param"},
+                new CommandLineInput(
+                    new[] {"param"})
+            );
+
+            yield return new TestCaseData(
+                new[] {"cmd", "param"},
+                new CommandLineInput(
+                    new[] {"cmd", "param"})
+            );
+
+            yield return new TestCaseData(
+                new[] {"--option", "value"},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput("option", "value")
+                    })
+            );
+
+            yield return new TestCaseData(
+                new[] {"--option1", "value1", "--option2", "value2"},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput("option1", "value1"),
+                        new CommandOptionInput("option2", "value2")
+                    })
+            );
+
+            yield return new TestCaseData(
+                new[] {"--option", "value1", "value2"},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput("option", new[] {"value1", "value2"})
+                    })
+            );
+
+            yield return new TestCaseData(
+                new[] {"--option", "value1", "--option", "value2"},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput("option", new[] {"value1", "value2"})
+                    })
+            );
+
+            yield return new TestCaseData(
+                new[] {"-a", "value"},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput("a", "value")
+                    })
+            );
+
+            yield return new TestCaseData(
+                new[] {"-a", "value1", "-b", "value2"},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput("a", "value1"),
+                        new CommandOptionInput("b", "value2")
+                    })
+            );
+
+            yield return new TestCaseData(
+                new[] {"-a", "value1", "value2"},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput("a", new[] {"value1", "value2"})
+                    })
+            );
+
+            yield return new TestCaseData(
+                new[] {"-a", "value1", "-a", "value2"},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput("a", new[] {"value1", "value2"})
+                    })
+            );
+
+            yield return new TestCaseData(
+                new[] {"--option1", "value1", "-b", "value2"},
+                new CommandLineInput(
+                    new[]
+                    {
+                        new CommandOptionInput("option1", "value1"),
+                        new CommandOptionInput("b", "value2")
+                    })
+            );
+
+            yield return new TestCaseData(
+                new[] {"--switch"},
+                new CommandLineInput(
+                    new[]
+                {
+                    new CommandOptionInput("switch")
+                })
+            );
+
+            yield return new TestCaseData(
+                new[] {"--switch1", "--switch2"},
+                new CommandLineInput(
+                    new[]
+                {
+                    new CommandOptionInput("switch1"),
+                    new CommandOptionInput("switch2")
+                })
+            );
+
+            yield return new TestCaseData(
+                new[] {"-s"},
+                new CommandLineInput(
+                    new[]
+                {
+                    new CommandOptionInput("s")
+                })
+            );
+
+            yield return new TestCaseData(
+                new[] {"-a", "-b"},
+                new CommandLineInput(
+                    new[]
+                {
+                    new CommandOptionInput("a"),
+                    new CommandOptionInput("b")
+                })
+            );
+
+            yield return new TestCaseData(
+                new[] {"-ab"},
+                new CommandLineInput(
+                    new[]
+                {
+                    new CommandOptionInput("a"),
+                    new CommandOptionInput("b")
+                })
+            );
+
+            yield return new TestCaseData(
+                new[] {"-ab", "value"},
+                new CommandLineInput(
+                    new[]
+                {
+                    new CommandOptionInput("a"),
+                    new CommandOptionInput("b", "value")
+                })
+            );
+
+            yield return new TestCaseData(
+                new[] {"cmd", "--option", "value"},
+                new CommandLineInput(
+                    new[] {"cmd"},
+                    new[]
+                {
+                    new CommandOptionInput("option", "value")
+                })
+            );
+
+            yield return new TestCaseData(
+                new[] {"[debug]"},
+                new CommandLineInput(
+                    new[] {"debug"},
+                    new string[0],
+                    new CommandOptionInput[0])
+            );
+
+            yield return new TestCaseData(
+                new[] {"[debug]", "[preview]"},
+                new CommandLineInput(
+                    new[] {"debug", "preview"},
+                    new string[0],
+                    new CommandOptionInput[0])
+            );
+
+            yield return new TestCaseData(
+                new[] {"cmd", "param1", "param2", "--option", "value"},
+                new CommandLineInput(
+                    new[] {"cmd", "param1", "param2"},
+                    new[]
+                {
+                    new CommandOptionInput("option", "value")
+                })
+            );
+
+            yield return new TestCaseData(
+                new[] {"[debug]", "[preview]", "-o", "value"},
+                new CommandLineInput(
+                    new[] {"debug", "preview"},
+                    new string[0],
+                    new[]
+                    {
+                        new CommandOptionInput("o", "value")
+                    })
+            );
+
+            yield return new TestCaseData(
+                new[] {"cmd", "[debug]", "[preview]", "-o", "value"},
+                new CommandLineInput(
+                    new[] {"debug", "preview"},
+                    new[] {"cmd"},
+                    new[]
+                    {
+                        new CommandOptionInput("o", "value")
+                    })
+            );
+
+            yield return new TestCaseData(
+                new[] {"cmd", "[debug]", "[preview]", "-o", "value"},
+                new CommandLineInput(
+                    new[] {"debug", "preview"},
+                    new[] {"cmd"},
+                    new[]
+                    {
+                        new CommandOptionInput("o", "value")
+                    })
+            );
+
+            yield return new TestCaseData(
+                new[] {"cmd", "param", "[debug]", "[preview]", "-o", "value"},
+                new CommandLineInput(
+                    new[] {"debug", "preview"},
+                    new[] {"cmd", "param"},
+                    new[]
+                    {
+                        new CommandOptionInput("o", "value")
+                    })
+            );
+        }
+
+        [Test]
+        [TestCaseSource(nameof(GetTestCases_Parse))]
+        public void Parse_Test(IReadOnlyList<string> commandLineArguments, CommandLineInput expectedResult)
+        {
+            // Act
+            var result = CommandLineInput.Parse(commandLineArguments);
+
+            // Assert
+            result.Should().BeEquivalentTo(expectedResult);
+        }
+    }
+}

CliFx.Tests/DummyTests.cs

@@ -1,4 +1,8 @@
-using System.Threading.Tasks;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Reflection;
+using System.Threading.Tasks;
 using CliWrap;
 using FluentAssertions;
 using NUnit.Framework;
@@ -8,66 +12,71 @@ namespace CliFx.Tests
     [TestFixture]
     public class DummyTests
     {
-        private static string DummyFilePath => typeof(Dummy.Program).Assembly.Location;
+        private static Assembly DummyAssembly { get; } = typeof(Dummy.Program).Assembly;
 
-        private static string DummyVersionText => typeof(Dummy.Program).Assembly.GetName().Version.ToString();
-
-        [Test]
-        [TestCase("", "Hello world")]
-        [TestCase("-t .NET", "Hello .NET")]
-        [TestCase("-e", "Hello world!")]
-        [TestCase("sum -v 1 2", "3")]
-        [TestCase("sum -v 2.75 3.6 4.18", "10.53")]
-        [TestCase("sum -v 4 -v 16", "20")]
-        [TestCase("sum --values 2 5 --values 3", "10")]
-        [TestCase("log -v 100", "2")]
-        [TestCase("log --value 256 --base 2", "8")]
-        public async Task CliApplication_RunAsync_Test(string arguments, string expectedOutput)
+        private static IEnumerable<TestCaseData> GetTestCases_RunAsync()
         {
-            // Arrange & Act
-            var result = await Cli.Wrap(DummyFilePath)
-                .SetArguments(arguments)
+            yield return new TestCaseData(
+                new[] {"--version"},
+                new Dictionary<string, string>(),
+                $"v{DummyAssembly.GetName().Version}"
+            );
+
+            yield return new TestCaseData(
+                new string[0],
+                new Dictionary<string, string>(),
+                "Hello World!"
+            );
+
+            yield return new TestCaseData(
+                new[] {"--target", "Earth"},
+                new Dictionary<string, string>(),
+                "Hello Earth!"
+            );
+
+            yield return new TestCaseData(
+                new string[0],
+                new Dictionary<string, string>
+                {
+                    ["ENV_TARGET"] = "Mars"
+                },
+                "Hello Mars!"
+            );
+
+            yield return new TestCaseData(
+                new[] {"--target", "Earth"},
+                new Dictionary<string, string>
+                {
+                    ["ENV_TARGET"] = "Mars"
+                },
+                "Hello Earth!"
+            );
+        }
+
+        [TestCaseSource(nameof(GetTestCases_RunAsync))]
+        public async Task RunAsync_Test(
+            IReadOnlyList<string> arguments,
+            IReadOnlyDictionary<string, string> environmentVariables,
+            string expectedStdOut)
+        {
+            // Arrange
+            var cli = Cli.Wrap("dotnet")
+                .SetArguments(arguments.Prepend(DummyAssembly.Location).ToArray())
                 .EnableExitCodeValidation()
                 .EnableStandardErrorValidation()
-                .ExecuteAsync();
+                .SetStandardOutputCallback(Console.WriteLine)
+                .SetStandardErrorCallback(Console.WriteLine);
+
+            foreach (var (key, value) in environmentVariables)
+                cli.SetEnvironmentVariable(key, value);
+
+            // Act
+            var result = await cli.ExecuteAsync();
 
             // Assert
-            result.StandardOutput.Trim().Should().Be(expectedOutput);
-        }
-
-        [Test]
-        [TestCase("--version")]
-        public async Task CliApplication_RunAsync_ShowVersion_Test(string arguments)
-        {
-            // Arrange & Act
-            var result = await Cli.Wrap(DummyFilePath)
-                .SetArguments(arguments)
-                .EnableExitCodeValidation()
-                .EnableStandardErrorValidation()
-                .ExecuteAsync();
-
-            // Assert
-            result.StandardOutput.Trim().Should().Be(DummyVersionText);
-        }
-
-        [Test]
-        [TestCase("--help")]
-        [TestCase("-h")]
-        [TestCase("sum -h")]
-        [TestCase("sum --help")]
-        [TestCase("log -h")]
-        [TestCase("log --help")]
-        public async Task CliApplication_RunAsync_ShowHelp_Test(string arguments)
-        {
-            // Arrange & Act
-            var result = await Cli.Wrap(DummyFilePath)
-                .SetArguments(arguments)
-                .EnableExitCodeValidation()
-                .EnableStandardErrorValidation()
-                .ExecuteAsync();
-
-            // Assert
-            result.StandardOutput.Trim().Should().NotBeNullOrWhiteSpace();
+            result.ExitCode.Should().Be(0);
+            result.StandardError.Should().BeNullOrWhiteSpace();
+            result.StandardOutput.TrimEnd().Should().Be(expectedStdOut);
         }
     }
 }

CliFx.Tests/HelpTextRendererTests.Commands.cs

@@ -1,42 +0,0 @@
-using System.Threading.Tasks;
-using CliFx.Attributes;
-using CliFx.Services;
-
-namespace CliFx.Tests
-{
-    public partial class HelpTextRendererTests
-    {
-        [Command(Description = "DefaultCommand description.")]
-        private class DefaultCommand : ICommand
-        {
-            [CommandOption("option-a", 'a', Description = "OptionA description.")]
-            public string OptionA { get; set; }
-
-            [CommandOption("option-b", 'b', Description = "OptionB description.")]
-            public string OptionB { get; set; }
-
-            public Task ExecuteAsync(IConsole console) => Task.CompletedTask;
-        }
-
-        [Command("cmd", Description = "NamedCommand description.")]
-        private class NamedCommand : ICommand
-        {
-            [CommandOption("option-c", 'c', Description = "OptionC description.")]
-            public string OptionC { get; set; }
-
-            [CommandOption("option-d", 'd', Description = "OptionD description.")]
-            public string OptionD { get; set; }
-
-            public Task ExecuteAsync(IConsole console) => Task.CompletedTask;
-        }
-
-        [Command("cmd sub", Description = "NamedSubCommand description.")]
-        private class NamedSubCommand : ICommand
-        {
-            [CommandOption("option-e", 'e', Description = "OptionE description.")]
-            public string OptionE { get; set; }
-
-            public Task ExecuteAsync(IConsole console) => Task.CompletedTask;
-        }
-    }
-}

CliFx.Tests/HelpTextRendererTests.cs

@@ -1,105 +0,0 @@
-using System;
-using System.Collections.Generic;
-using System.IO;
-using System.Linq;
-using CliFx.Models;
-using CliFx.Services;
-using FluentAssertions;
-using NUnit.Framework;
-
-namespace CliFx.Tests
-{
-    [TestFixture]
-    public partial class HelpTextRendererTests
-    {
-        private static HelpTextSource CreateHelpTextSource(IReadOnlyList<Type> availableCommandTypes, Type targetCommandType)
-        {
-            var commandSchemaResolver = new CommandSchemaResolver();
-
-            var applicationMetadata = new ApplicationMetadata("TestApp", "testapp", "1.0", null);
-            var availableCommandSchemas = commandSchemaResolver.GetCommandSchemas(availableCommandTypes);
-            var targetCommandSchema = availableCommandSchemas.Single(s => s.Type == targetCommandType);
-
-            return new HelpTextSource(applicationMetadata, availableCommandSchemas, targetCommandSchema);
-        }
-
-        private static IEnumerable<TestCaseData> GetTestCases_RenderHelpText()
-        {
-            yield return new TestCaseData(
-                CreateHelpTextSource(
-                    new[] {typeof(DefaultCommand), typeof(NamedCommand), typeof(NamedSubCommand)},
-                    typeof(DefaultCommand)),
-
-                new[]
-                {
-                    "Usage",
-                    "[command]", "[options]",
-                    "Options",
-                    "-a|--option-a", "OptionA description.",
-                    "-b|--option-b", "OptionB description.",
-                    "-h|--help", "Shows help text.",
-                    "--version", "Shows version information.",
-                    "Commands",
-                    "cmd", "NamedCommand description.",
-                    "You can run", "to show help on a specific command."
-                }
-            );
-
-            yield return new TestCaseData(
-                CreateHelpTextSource(
-                    new[] {typeof(DefaultCommand), typeof(NamedCommand), typeof(NamedSubCommand)},
-                    typeof(NamedCommand)),
-
-                new[]
-                {
-                    "Description",
-                    "NamedCommand description.",
-                    "Usage",
-                    "cmd", "[command]", "[options]",
-                    "Options",
-                    "-c|--option-c", "OptionC description.",
-                    "-d|--option-d", "OptionD description.",
-                    "-h|--help", "Shows help text.",
-                    "Commands",
-                    "sub", "NamedSubCommand description.",
-                    "You can run", "to show help on a specific command."
-                }
-            );
-
-            yield return new TestCaseData(
-                CreateHelpTextSource(
-                    new[] {typeof(DefaultCommand), typeof(NamedCommand), typeof(NamedSubCommand)},
-                    typeof(NamedSubCommand)),
-
-                new[]
-                {
-                    "Description",
-                    "NamedSubCommand description.",
-                    "Usage",
-                    "cmd sub", "[options]",
-                    "Options",
-                    "-e|--option-e", "OptionE description.",
-                    "-h|--help", "Shows help text."
-                }
-            );
-        }
-
-        [Test]
-        [TestCaseSource(nameof(GetTestCases_RenderHelpText))]
-        public void RenderHelpText_Test(HelpTextSource source, IReadOnlyList<string> expectedSubstrings)
-        {
-            // Arrange
-            using (var stdout = new StringWriter())
-            {
-                var renderer = new HelpTextRenderer();
-                var console = new VirtualConsole(stdout);
-
-                // Act
-                renderer.RenderHelpText(console, source);
-
-                // Assert
-                stdout.ToString().Should().ContainAll(expectedSubstrings);
-            }
-        }
-    }
-}

CliFx.Tests/SystemConsoleTests.cs

@@ -0,0 +1,39 @@
+using System;
+using FluentAssertions;
+using NUnit.Framework;
+
+namespace CliFx.Tests
+{
+    [TestFixture]
+    public class SystemConsoleTests
+    {
+        [TearDown]
+        public void TearDown()
+        {
+            // Reset console color so it doesn't carry on into the next tests
+            Console.ResetColor();
+        }
+
+        [Test(Description = "Must be in sync with system console")]
+        public void Smoke_Test()
+        {
+            // Arrange
+            var console = new SystemConsole();
+
+            // Act
+            console.ResetColor();
+            console.ForegroundColor = ConsoleColor.DarkMagenta;
+            console.BackgroundColor = ConsoleColor.DarkMagenta;
+
+            // Assert
+            console.Input.Should().BeSameAs(Console.In);
+            console.IsInputRedirected.Should().Be(Console.IsInputRedirected);
+            console.Output.Should().BeSameAs(Console.Out);
+            console.IsOutputRedirected.Should().Be(Console.IsOutputRedirected);
+            console.Error.Should().BeSameAs(Console.Error);
+            console.IsErrorRedirected.Should().Be(Console.IsErrorRedirected);
+            console.ForegroundColor.Should().Be(Console.ForegroundColor);
+            console.BackgroundColor.Should().Be(Console.BackgroundColor);
+        }
+    }
+}

CliFx.Tests/TestCommands/AllRequiredOptionsCommand.cs

@@ -0,0 +1,17 @@
+using System.Threading.Tasks;
+using CliFx.Attributes;
+
+namespace CliFx.Tests.TestCommands
+{
+    [Command("allrequired", Description = "AllRequiredOptionsCommand description.")]
+    public class AllRequiredOptionsCommand : ICommand
+    {
+        [CommandOption("option-f", 'f', IsRequired = true, Description = "OptionF description.")]
+        public string? OptionF { get; set; }
+
+        [CommandOption("option-g", 'g', IsRequired = true, Description = "OptionG description.")]
+        public string? OptionFG { get; set; }
+
+        public ValueTask ExecuteAsync(IConsole console) => default;
+    }
+}

CliFx.Tests/TestCommands/AllSupportedTypesCommand.cs

@@ -0,0 +1,126 @@
+using System;
+using System.Collections;
+using System.Collections.Generic;
+using System.Threading.Tasks;
+using CliFx.Attributes;
+using CliFx.Tests.TestCustomTypes;
+
+namespace CliFx.Tests.TestCommands
+{
+    [Command]
+    public class AllSupportedTypesCommand : ICommand
+    {
+        [CommandOption(nameof(Object))]
+        public object? Object { get; set; } = 42;
+
+        [CommandOption(nameof(String))]
+        public string? String { get; set; } = "foo bar";
+
+        [CommandOption(nameof(Bool))]
+        public bool Bool { get; set; }
+
+        [CommandOption(nameof(Char))]
+        public char Char { get; set; }
+
+        [CommandOption(nameof(Sbyte))]
+        public sbyte Sbyte { get; set; }
+
+        [CommandOption(nameof(Byte))]
+        public byte Byte { get; set; }
+
+        [CommandOption(nameof(Short))]
+        public short Short { get; set; }
+
+        [CommandOption(nameof(Ushort))]
+        public ushort Ushort { get; set; }
+
+        [CommandOption(nameof(Int))]
+        public int Int { get; set; }
+
+        [CommandOption(nameof(Uint))]
+        public uint Uint { get; set; }
+
+        [CommandOption(nameof(Long))]
+        public long Long { get; set; }
+
+        [CommandOption(nameof(Ulong))]
+        public ulong Ulong { get; set; }
+
+        [CommandOption(nameof(Float))]
+        public float Float { get; set; }
+
+        [CommandOption(nameof(Double))]
+        public double Double { get; set; }
+
+        [CommandOption(nameof(Decimal))]
+        public decimal Decimal { get; set; }
+
+        [CommandOption(nameof(DateTime))]
+        public DateTime DateTime { get; set; }
+
+        [CommandOption(nameof(DateTimeOffset))]
+        public DateTimeOffset DateTimeOffset { get; set; }
+
+        [CommandOption(nameof(TimeSpan))]
+        public TimeSpan TimeSpan { get; set; }
+
+        [CommandOption(nameof(TestEnum))]
+        public TestEnum TestEnum { get; set; }
+
+        [CommandOption(nameof(IntNullable))]
+        public int? IntNullable { get; set; }
+
+        [CommandOption(nameof(TestEnumNullable))]
+        public TestEnum? TestEnumNullable { get; set; }
+
+        [CommandOption(nameof(TimeSpanNullable))]
+        public TimeSpan? TimeSpanNullable { get; set; }
+
+        [CommandOption(nameof(TestStringConstructable))]
+        public TestStringConstructable? TestStringConstructable { get; set; }
+
+        [CommandOption(nameof(TestStringParseable))]
+        public TestStringParseable? TestStringParseable { get; set; }
+
+        [CommandOption(nameof(TestStringParseableWithFormatProvider))]
+        public TestStringParseableWithFormatProvider? TestStringParseableWithFormatProvider { get; set; }
+
+        [CommandOption(nameof(ObjectArray))]
+        public object[]? ObjectArray { get; set; }
+
+        [CommandOption(nameof(StringArray))]
+        public string[]? StringArray { get; set; }
+
+        [CommandOption(nameof(IntArray))]
+        public int[]? IntArray { get; set; }
+
+        [CommandOption(nameof(TestEnumArray))]
+        public TestEnum[]? TestEnumArray { get; set; }
+
+        [CommandOption(nameof(IntNullableArray))]
+        public int?[]? IntNullableArray { get; set; }
+
+        [CommandOption(nameof(TestStringConstructableArray))]
+        public TestStringConstructable[]? TestStringConstructableArray { get; set; }
+
+        [CommandOption(nameof(Enumerable))]
+        public IEnumerable? Enumerable { get; set; }
+
+        [CommandOption(nameof(StringEnumerable))]
+        public IEnumerable<string>? StringEnumerable { get; set; }
+
+        [CommandOption(nameof(StringReadOnlyList))]
+        public IReadOnlyList<string>? StringReadOnlyList { get; set; }
+
+        [CommandOption(nameof(StringList))]
+        public List<string>? StringList { get; set; }
+
+        [CommandOption(nameof(StringHashSet))]
+        public HashSet<string>? StringHashSet { get; set; }
+
+        [CommandOption(nameof(NonConvertible))]
+        public TestNonStringParseable? NonConvertible { get; set; }
+
+        public ValueTask ExecuteAsync(IConsole console) => default;
+    }
+}

CliFx.Tests/TestCommands/BrokenEnumerableCommand.cs

@@ -0,0 +1,15 @@
+using System.Threading.Tasks;
+using CliFx.Attributes;
+using CliFx.Tests.TestCustomTypes;
+
+namespace CliFx.Tests.TestCommands
+{
+    [Command]
+    public class BrokenEnumerableCommand : ICommand
+    {
+        [CommandParameter(0)]
+        public TestCustomEnumerable<string>? Test { get; set; }
+
+        public ValueTask ExecuteAsync(IConsole console) => default;
+    }
+}

CliFx.Tests/TestCommands/CancellableCommand.cs

@@ -0,0 +1,16 @@
+using System;
+using System.Threading.Tasks;
+using CliFx.Attributes;
+
+namespace CliFx.Tests.TestCommands
+{
+    [Command("cancel")]
+    public class CancellableCommand : ICommand
+    {
+        public async ValueTask ExecuteAsync(IConsole console)
+        {
+            await Task.Delay(TimeSpan.FromSeconds(3), console.GetCancellationToken());
+            console.Output.WriteLine("Never printed");
+        }
+    }
+}

CliFx.Tests/TestCommands/CommandExceptionCommand.cs

@@ -0,0 +1,18 @@
+using System.Threading.Tasks;
+using CliFx.Attributes;
+using CliFx.Exceptions;
+
+namespace CliFx.Tests.TestCommands
+{
+    [Command("exc")]
+    public class CommandExceptionCommand : ICommand
+    {
+        [CommandOption("code", 'c')]
+        public int ExitCode { get; set; } = 1337;
+        
+        [CommandOption("msg", 'm')]
+        public string? Message { get; set; }
+        
+        public ValueTask ExecuteAsync(IConsole console) => throw new CommandException(Message, ExitCode);
+    }
+}

CliFx.Tests/TestCommands/ConcatCommand.cs

@@ -0,0 +1,22 @@
+using System.Collections.Generic;
+using System.Threading.Tasks;
+using CliFx.Attributes;
+
+namespace CliFx.Tests.TestCommands
+{
+    [Command("concat", Description = "Concatenate strings.")]
+    public class ConcatCommand : ICommand
+    {
+        [CommandOption('i', IsRequired = true, Description = "Input strings.")]
+        public IReadOnlyList<string> Inputs { get; set; }
+
+        [CommandOption('s', Description = "String separator.")]
+        public string Separator { get; set; } = ""; 
+        
+        public ValueTask ExecuteAsync(IConsole console)
+        {
+            console.Output.WriteLine(string.Join(Separator, Inputs));
+            return default;
+        }
+    }
+}

CliFx.Tests/TestCommands/DivideCommand.cs

@@ -0,0 +1,24 @@
+using System.Threading.Tasks;
+using CliFx.Attributes;
+
+namespace CliFx.Tests.TestCommands
+{
+    [Command("div", Description = "Divide one number by another.")]
+    public class DivideCommand : ICommand
+    {
+        [CommandOption("dividend", 'D', IsRequired = true, Description = "The number to divide.")]
+        public double Dividend { get; set; }
+
+        [CommandOption("divisor", 'd', IsRequired = true, Description = "The number to divide by.")]
+        public double Divisor { get; set; }
+
+        // This property should be ignored by resolver
+        public bool NotAnOption { get; set; }
+        
+        public ValueTask ExecuteAsync(IConsole console)
+        {
+            console.Output.WriteLine(Dividend / Divisor);
+            return default;
+        }
+    }
+}

CliFx.Tests/TestCommands/DuplicateOptionEnvironmentVariableNamesCommand.cs

@@ -0,0 +1,17 @@
+using System.Threading.Tasks;
+using CliFx.Attributes;
+
+namespace CliFx.Tests.TestCommands
+{
+    [Command]
+    public class DuplicateOptionEnvironmentVariableNamesCommand : ICommand
+    {
+        [CommandOption("option-a", EnvironmentVariableName = "ENV_VAR")]
+        public string? OptionA { get; set; }
+
+        [CommandOption("option-b", EnvironmentVariableName = "ENV_VAR")]
+        public string? OptionB { get; set; }
+
+        public ValueTask ExecuteAsync(IConsole console) => default;
+    }
+}

CliFx.Tests/TestCommands/DuplicateOptionNamesCommand.cs

@@ -0,0 +1,17 @@
+using System.Threading.Tasks;
+using CliFx.Attributes;
+
+namespace CliFx.Tests.TestCommands
+{
+    [Command]
+    public class DuplicateOptionNamesCommand : ICommand
+    {
+        [CommandOption("fruits")]
+        public string? Apples { get; set; }
+        
+        [CommandOption("fruits")]
+        public string? Oranges { get; set; }
+        
+        public ValueTask ExecuteAsync(IConsole console) => default;
+    }
+}

CliFx.Tests/TestCommands/DuplicateOptionShortNamesCommand.cs

@@ -0,0 +1,17 @@
+using System.Threading.Tasks;
+using CliFx.Attributes;
+
+namespace CliFx.Tests.TestCommands
+{
+    [Command]
+    public class DuplicateOptionShortNamesCommand : ICommand
+    {
+        [CommandOption('x')]
+        public string? OptionA { get; set; }
+
+        [CommandOption('x')]
+        public string? OptionB { get; set; }
+
+        public ValueTask ExecuteAsync(IConsole console) => default;
+    }
+}

CliFx.Tests/TestCommands/DuplicateParameterNameCommand.cs

@@ -0,0 +1,17 @@
+using System.Threading.Tasks;
+using CliFx.Attributes;
+
+namespace CliFx.Tests.TestCommands
+{
+    [Command]
+    public class DuplicateParameterNameCommand : ICommand
+    {
+        [CommandParameter(0, Name = "param")]
+        public string? ParameterA { get; set; }
+
+        [CommandParameter(1, Name = "param")]
+        public string? ParameterB { get; set; }
+
+        public ValueTask ExecuteAsync(IConsole console) => default;
+    }
+}

CliFx.Tests/TestCommands/DuplicateParameterOrderCommand.cs

@@ -0,0 +1,17 @@
+using System.Threading.Tasks;
+using CliFx.Attributes;
+
+namespace CliFx.Tests.TestCommands
+{
+    [Command]
+    public class DuplicateParameterOrderCommand : ICommand
+    {
+        [CommandParameter(13)]
+        public string? ParameterA { get; set; }
+
+        [CommandParameter(13)]
+        public string? ParameterB { get; set; }
+
+        public ValueTask ExecuteAsync(IConsole console) => default;
+    }
+}

CliFx.Tests/TestCommands/EnvironmentVariableCommand.cs

@@ -0,0 +1,14 @@
+using System.Threading.Tasks;
+using CliFx.Attributes;
+
+namespace CliFx.Tests.TestCommands
+{
+	[Command(Description = "Reads option values from environment variables.")]
+	public class EnvironmentVariableCommand : ICommand
+	{
+		[CommandOption("opt", EnvironmentVariableName = "ENV_SINGLE_VALUE")]
+		public string? Option { get; set; }
+
+		public ValueTask ExecuteAsync(IConsole console) => default;
+	}
+}

CliFx.Tests/TestCommands/EnvironmentVariableWithMultipleValuesCommand.cs

@@ -0,0 +1,15 @@
+using System.Collections.Generic;
+using System.Threading.Tasks;
+using CliFx.Attributes;
+
+namespace CliFx.Tests.TestCommands
+{
+	[Command(Description = "Reads multiple option values from environment variables.")]
+	public class EnvironmentVariableWithMultipleValuesCommand : ICommand
+	{
+		[CommandOption("opt", EnvironmentVariableName = "ENV_MULTIPLE_VALUES")]
+		public IEnumerable<string>? Option { get; set; }
+
+		public ValueTask ExecuteAsync(IConsole console) => default;
+	}
+}

CliFx.Tests/TestCommands/EnvironmentVariableWithoutCollectionPropertyCommand.cs

@@ -0,0 +1,14 @@
+using System.Threading.Tasks;
+using CliFx.Attributes;
+
+namespace CliFx.Tests.TestCommands
+{
+    [Command(Description = "Reads one option value from environment variables because target property is not a collection.")]
+    public class EnvironmentVariableWithoutCollectionPropertyCommand : ICommand
+    {
+        [CommandOption("opt", EnvironmentVariableName = "ENV_MULTIPLE_VALUES")]
+        public string? Option { get; set; }
+
+        public ValueTask ExecuteAsync(IConsole console) => default;
+    }
+}

CliFx.Tests/TestCommands/ExceptionCommand.cs

@@ -0,0 +1,15 @@
+using System;
+using System.Threading.Tasks;
+using CliFx.Attributes;
+
+namespace CliFx.Tests.TestCommands
+{
+    [Command("exc")]
+    public class ExceptionCommand : ICommand
+    {
+        [CommandOption("msg", 'm')]
+        public string? Message { get; set; }
+        
+        public ValueTask ExecuteAsync(IConsole console) => throw new Exception(Message);
+    }
+}

CliFx.Tests/TestCommands/HelloWorldDefaultCommand.cs

@@ -0,0 +1,15 @@
+using System.Threading.Tasks;
+using CliFx.Attributes;
+
+namespace CliFx.Tests.TestCommands
+{
+    [Command]
+    public class HelloWorldDefaultCommand : ICommand
+    {
+        public ValueTask ExecuteAsync(IConsole console)
+        {
+            console.Output.WriteLine("Hello world.");
+            return default;
+        }
+    }
+}

CliFx.Tests/TestCommands/HelpDefaultCommand.cs

@@ -0,0 +1,17 @@
+using System.Threading.Tasks;
+using CliFx.Attributes;
+
+namespace CliFx.Tests.TestCommands
+{
+    [Command(Description = "HelpDefaultCommand description.")]
+    public class HelpDefaultCommand : ICommand
+    {
+        [CommandOption("option-a", 'a', Description = "OptionA description.")]
+        public string? OptionA { get; set; }
+
+        [CommandOption("option-b", 'b', Description = "OptionB description.")]
+        public string? OptionB { get; set; }
+
+        public ValueTask ExecuteAsync(IConsole console) => default;
+    }
+}

CliFx.Tests/TestCommands/HelpNamedCommand.cs

@@ -0,0 +1,17 @@
+using System.Threading.Tasks;
+using CliFx.Attributes;
+
+namespace CliFx.Tests.TestCommands
+{
+    [Command("cmd", Description = "HelpNamedCommand description.")]
+    public class HelpNamedCommand : ICommand
+    {
+        [CommandOption("option-c", 'c', Description = "OptionC description.")]
+        public string? OptionC { get; set; }
+
+        [CommandOption("option-d", 'd', Description = "OptionD description.")]
+        public string? OptionD { get; set; }
+
+        public ValueTask ExecuteAsync(IConsole console) => default;
+    }
+}

CliFx.Tests/TestCommands/HelpSubCommand.cs

@@ -0,0 +1,14 @@
+using System.Threading.Tasks;
+using CliFx.Attributes;
+
+namespace CliFx.Tests.TestCommands
+{
+    [Command("cmd sub", Description = "HelpSubCommand description.")]
+    public class HelpSubCommand : ICommand
+    {
+        [CommandOption("option-e", 'e', Description = "OptionE description.")]
+        public string? OptionE { get; set; }
+
+        public ValueTask ExecuteAsync(IConsole console) => default;
+    }
+}

CliFx.Tests/TestCommands/MultipleNonScalarParametersCommand.cs

@@ -0,0 +1,18 @@
+using System.Collections.Generic;
+using System.Threading.Tasks;
+using CliFx.Attributes;
+
+namespace CliFx.Tests.TestCommands
+{
+    [Command]
+    public class MultipleNonScalarParametersCommand : ICommand
+    {
+        [CommandParameter(0)]
+        public IReadOnlyList<string>? ParameterA { get; set; }
+
+        [CommandParameter(1)]
+        public IReadOnlyList<string>? ParameterB { get; set; }
+
+        public ValueTask ExecuteAsync(IConsole console) => default;
+    }
+}

CliFx.Tests/TestCommands/NonAnnotatedCommand.cs

@@ -0,0 +1,9 @@
+using System.Threading.Tasks;
+
+namespace CliFx.Tests.TestCommands
+{
+    public class NonAnnotatedCommand : ICommand
+    {
+        public ValueTask ExecuteAsync(IConsole console) => default;
+    }
+}

CliFx.Tests/TestCommands/NonImplementedCommand.cs

@@ -0,0 +1,9 @@
+using CliFx.Attributes;
+
+namespace CliFx.Tests.TestCommands
+{
+    [Command]
+    public class NonImplementedCommand
+    {
+    }
+}

CliFx.Tests/TestCommands/NonLastNonScalarParameterCommand.cs

@@ -0,0 +1,18 @@
+using System.Collections.Generic;
+using System.Threading.Tasks;
+using CliFx.Attributes;
+
+namespace CliFx.Tests.TestCommands
+{
+    [Command]
+    public class NonLastNonScalarParameterCommand : ICommand
+    {
+        [CommandParameter(0)]
+        public IReadOnlyList<string>? ParameterA { get; set; }
+
+        [CommandParameter(1)]
+        public string? ParameterB { get; set; }
+
+        public ValueTask ExecuteAsync(IConsole console) => default;
+    }
+}

CliFx.Tests/TestCommands/ParameterCommand.cs

@@ -0,0 +1,24 @@
+using System.Collections.Generic;
+using System.Threading.Tasks;
+using CliFx.Attributes;
+
+namespace CliFx.Tests.TestCommands
+{
+    [Command("param cmd", Description = "Command using positional parameters")]
+    public class ParameterCommand : ICommand
+    {
+        [CommandParameter(0, Name = "first")]
+        public string? ParameterA { get; set; }
+
+        [CommandParameter(10)]
+        public int? ParameterB { get; set; }
+
+        [CommandParameter(20, Description = "A list of numbers", Name = "third list")]
+        public IEnumerable<int>? ParameterC { get; set; }
+
+        [CommandOption("option", 'o')]
+        public string? OptionA { get; set; }
+
+        public ValueTask ExecuteAsync(IConsole console) => default;
+    }
+}

CliFx.Tests/TestCommands/SimpleParameterCommand.cs

@@ -0,0 +1,20 @@
+using System.Threading.Tasks;
+using CliFx.Attributes;
+
+namespace CliFx.Tests.TestCommands
+{
+    [Command("param cmd2", Description = "Command using positional parameters")]
+    public class SimpleParameterCommand : ICommand
+    {
+        [CommandParameter(0, Name = "first")]
+        public string? ParameterA { get; set; }
+
+        [CommandParameter(10)]
+        public int? ParameterB { get; set; }
+
+        [CommandOption("option", 'o')]
+        public string? OptionA { get; set; }
+
+        public ValueTask ExecuteAsync(IConsole console) => default;
+    }
+}

CliFx.Tests/TestCommands/SomeRequiredOptionsCommand.cs

@@ -0,0 +1,17 @@
+using System.Threading.Tasks;
+using CliFx.Attributes;
+
+namespace CliFx.Tests.TestCommands
+{
+    [Command("somerequired", Description = "SomeRequiredOptionsCommand description.")]
+    public class SomeRequiredOptionsCommand : ICommand
+    {
+        [CommandOption("option-f", 'f', IsRequired = true, Description = "OptionF description.")]
+        public string? OptionF { get; set; }
+
+        [CommandOption("option-g", 'g', Description = "OptionG description.")]
+        public string? OptionFG { get; set; }
+
+        public ValueTask ExecuteAsync(IConsole console) => default;
+    }
+}

CliFx.Tests/TestCustomTypes/TestCustomEnumerable.cs

@@ -0,0 +1,14 @@
+using System.Collections;
+using System.Collections.Generic;
+
+namespace CliFx.Tests.TestCustomTypes
+{
+    public class TestCustomEnumerable<T> : IEnumerable<T>
+    {
+        private readonly T[] _arr = new T[0];
+
+        public IEnumerator<T> GetEnumerator() => ((IEnumerable<T>) _arr).GetEnumerator();
+
+        IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
+    }
+}

CliFx.Tests/TestCustomTypes/TestEnum.cs

@@ -0,0 +1,9 @@
+namespace CliFx.Tests.TestCustomTypes
+{
+    public enum TestEnum
+    {
+        Value1,
+        Value2,
+        Value3
+    }
+}

CliFx.Tests/TestCustomTypes/TestNonStringParseable.cs

@@ -0,0 +1,12 @@
+namespace CliFx.Tests.TestCustomTypes
+{
+    public class TestNonStringParseable
+    {
+        public int Value { get; }
+
+        public TestNonStringParseable(int value)
+        {
+            Value = value;
+        }
+    }
+}

CliFx.Tests/TestCustomTypes/TestStringConstructable.cs

@@ -0,0 +1,12 @@
+namespace CliFx.Tests.TestCustomTypes
+{
+    public class TestStringConstructable
+    {
+        public string Value { get; }
+
+        public TestStringConstructable(string value)
+        {
+            Value = value;
+        }
+    }
+}

CliFx.Tests/TestCustomTypes/TestStringParseable.cs

@@ -0,0 +1,14 @@
+namespace CliFx.Tests.TestCustomTypes
+{
+    public class TestStringParseable
+    {
+        public string Value { get; }
+
+        private TestStringParseable(string value)
+        {
+            Value = value;
+        }
+
+        public static TestStringParseable Parse(string value) => new TestStringParseable(value);
+    }
+}

CliFx.Tests/TestCustomTypes/TestStringParseableWithFormatProvider.cs

@@ -0,0 +1,17 @@
+using System;
+
+namespace CliFx.Tests.TestCustomTypes
+{
+    public class TestStringParseableWithFormatProvider
+    {
+        public string Value { get; }
+
+        private TestStringParseableWithFormatProvider(string value)
+        {
+            Value = value;
+        }
+
+        public static TestStringParseableWithFormatProvider Parse(string value, IFormatProvider formatProvider) =>
+            new TestStringParseableWithFormatProvider(value + " " + formatProvider);
+    }
+}

CliFx.Tests/Utilities/ProgressTickerTests.cs

@@ -0,0 +1,54 @@
+using System.Globalization;
+using System.IO;
+using System.Linq;
+using CliFx.Utilities;
+using FluentAssertions;
+using NUnit.Framework;
+
+namespace CliFx.Tests.Utilities
+{
+    [TestFixture]
+    public class ProgressTickerTests
+    {
+        [Test]
+        public void Report_Test()
+        {
+            // Arrange
+            var formatProvider = CultureInfo.InvariantCulture;
+
+            using var stdout = new StringWriter(formatProvider);
+
+            var console = new VirtualConsole(TextReader.Null, false, stdout, false, TextWriter.Null, false);
+            var ticker = console.CreateProgressTicker();
+
+            var progressValues = Enumerable.Range(0, 100).Select(p => p / 100.0).ToArray();
+            var progressStringValues = progressValues.Select(p => p.ToString("P2", formatProvider)).ToArray();
+
+            // Act
+            foreach (var progress in progressValues)
+                ticker.Report(progress);
+
+            // Assert
+            stdout.ToString().Should().ContainAll(progressStringValues);
+        }
+
+        [Test]
+        public void Report_Redirected_Test()
+        {
+            // Arrange
+            using var stdout = new StringWriter();
+
+            var console = new VirtualConsole(stdout);
+            var ticker = console.CreateProgressTicker();
+
+            var progressValues = Enumerable.Range(0, 100).Select(p => p / 100.0).ToArray();
+
+            // Act
+            foreach (var progress in progressValues)
+                ticker.Report(progress);
+
+            // Assert
+            stdout.ToString().Should().BeEmpty();
+        }
+    }
+}

CliFx.Tests/VirtualConsoleTests.cs

@@ -0,0 +1,40 @@
+using System;
+using System.IO;
+using FluentAssertions;
+using NUnit.Framework;
+
+namespace CliFx.Tests
+{
+    [TestFixture]
+    public class VirtualConsoleTests
+    {
+        [Test(Description = "Must not leak to system console")]
+        public void Smoke_Test()
+        {
+            // Arrange
+            using var stdin = new StringReader("hello world");
+            using var stdout = new StringWriter();
+            using var stderr = new StringWriter();
+
+            var console = new VirtualConsole(stdin, stdout, stderr);
+
+            // Act
+            console.ResetColor();
+            console.ForegroundColor = ConsoleColor.DarkMagenta;
+            console.BackgroundColor = ConsoleColor.DarkMagenta;
+
+            // Assert
+            console.Input.Should().BeSameAs(stdin);
+            console.Input.Should().NotBeSameAs(Console.In);
+            console.IsInputRedirected.Should().BeTrue();
+            console.Output.Should().BeSameAs(stdout);
+            console.Output.Should().NotBeSameAs(Console.Out);
+            console.IsOutputRedirected.Should().BeTrue();
+            console.Error.Should().BeSameAs(stderr);
+            console.Error.Should().NotBeSameAs(Console.Error);
+            console.IsErrorRedirected.Should().BeTrue();
+            console.ForegroundColor.Should().NotBe(Console.ForegroundColor);
+            console.BackgroundColor.Should().NotBe(Console.BackgroundColor);
+        }
+    }
+}

CliFx.props

@@ -0,0 +1,11 @@
+<Project>
+
+  <PropertyGroup>
+    <Version>1.0</Version>
+    <Company>Tyrrrz</Company>
+    <Copyright>Copyright (C) Alexey Golub</Copyright>
+    <LangVersion>latest</LangVersion>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>

CliFx.sln

@@ -7,18 +7,19 @@ Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "CliFx", "CliFx\CliFx.csproj
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "CliFx.Tests", "CliFx.Tests\CliFx.Tests.csproj", "{268CF863-65A5-49BB-93CF-08972B7756DC}"
 EndProject
-Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "CliFx.Tests.Dummy", "CliFx.Tests.Dummy\CliFx.Tests.Dummy.csproj", "{4904B3EB-3286-4F1B-8B74-6FF051C8E787}"
-EndProject
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Solution Items", "Solution Items", "{3AAE8166-BB8E-49DA-844C-3A0EE6BD40A0}"
 	ProjectSection(SolutionItems) = preProject
 		Changelog.md = Changelog.md
 		License.txt = License.txt
 		Readme.md = Readme.md
+		CliFx.props = CliFx.props
 	EndProjectSection
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "CliFx.Benchmarks", "CliFx.Benchmarks\CliFx.Benchmarks.csproj", "{8ACD6DC2-D768-4850-9223-5B7C83A78513}"
 EndProject
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "CliFx.Demo", "CliFx.Demo\CliFx.Demo.csproj", "{AAB6844C-BF71-448F-A11B-89AEE459AB15}"
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "CliFx.Demo", "CliFx.Demo\CliFx.Demo.csproj", "{AAB6844C-BF71-448F-A11B-89AEE459AB15}"
+EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "CliFx.Tests.Dummy", "CliFx.Tests.Dummy\CliFx.Tests.Dummy.csproj", "{F717347D-8656-44DA-A4A2-BE515E8C4655}"
 EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
@@ -54,18 +55,6 @@ Global
 		{268CF863-65A5-49BB-93CF-08972B7756DC}.Release|x64.Build.0 = Release|Any CPU
 		{268CF863-65A5-49BB-93CF-08972B7756DC}.Release|x86.ActiveCfg = Release|Any CPU
 		{268CF863-65A5-49BB-93CF-08972B7756DC}.Release|x86.Build.0 = Release|Any CPU
-		{4904B3EB-3286-4F1B-8B74-6FF051C8E787}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
-		{4904B3EB-3286-4F1B-8B74-6FF051C8E787}.Debug|Any CPU.Build.0 = Debug|Any CPU
-		{4904B3EB-3286-4F1B-8B74-6FF051C8E787}.Debug|x64.ActiveCfg = Debug|Any CPU
-		{4904B3EB-3286-4F1B-8B74-6FF051C8E787}.Debug|x64.Build.0 = Debug|Any CPU
-		{4904B3EB-3286-4F1B-8B74-6FF051C8E787}.Debug|x86.ActiveCfg = Debug|Any CPU
-		{4904B3EB-3286-4F1B-8B74-6FF051C8E787}.Debug|x86.Build.0 = Debug|Any CPU
-		{4904B3EB-3286-4F1B-8B74-6FF051C8E787}.Release|Any CPU.ActiveCfg = Release|Any CPU
-		{4904B3EB-3286-4F1B-8B74-6FF051C8E787}.Release|Any CPU.Build.0 = Release|Any CPU
-		{4904B3EB-3286-4F1B-8B74-6FF051C8E787}.Release|x64.ActiveCfg = Release|Any CPU
-		{4904B3EB-3286-4F1B-8B74-6FF051C8E787}.Release|x64.Build.0 = Release|Any CPU
-		{4904B3EB-3286-4F1B-8B74-6FF051C8E787}.Release|x86.ActiveCfg = Release|Any CPU
-		{4904B3EB-3286-4F1B-8B74-6FF051C8E787}.Release|x86.Build.0 = Release|Any CPU
 		{8ACD6DC2-D768-4850-9223-5B7C83A78513}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
 		{8ACD6DC2-D768-4850-9223-5B7C83A78513}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{8ACD6DC2-D768-4850-9223-5B7C83A78513}.Debug|x64.ActiveCfg = Debug|Any CPU
@@ -90,6 +79,18 @@ Global
 		{AAB6844C-BF71-448F-A11B-89AEE459AB15}.Release|x64.Build.0 = Release|Any CPU
 		{AAB6844C-BF71-448F-A11B-89AEE459AB15}.Release|x86.ActiveCfg = Release|Any CPU
 		{AAB6844C-BF71-448F-A11B-89AEE459AB15}.Release|x86.Build.0 = Release|Any CPU
+		{F717347D-8656-44DA-A4A2-BE515E8C4655}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{F717347D-8656-44DA-A4A2-BE515E8C4655}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{F717347D-8656-44DA-A4A2-BE515E8C4655}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{F717347D-8656-44DA-A4A2-BE515E8C4655}.Debug|x64.Build.0 = Debug|Any CPU
+		{F717347D-8656-44DA-A4A2-BE515E8C4655}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{F717347D-8656-44DA-A4A2-BE515E8C4655}.Debug|x86.Build.0 = Debug|Any CPU
+		{F717347D-8656-44DA-A4A2-BE515E8C4655}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{F717347D-8656-44DA-A4A2-BE515E8C4655}.Release|Any CPU.Build.0 = Release|Any CPU
+		{F717347D-8656-44DA-A4A2-BE515E8C4655}.Release|x64.ActiveCfg = Release|Any CPU
+		{F717347D-8656-44DA-A4A2-BE515E8C4655}.Release|x64.Build.0 = Release|Any CPU
+		{F717347D-8656-44DA-A4A2-BE515E8C4655}.Release|x86.ActiveCfg = Release|Any CPU
+		{F717347D-8656-44DA-A4A2-BE515E8C4655}.Release|x86.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE

CliFx/ApplicationConfiguration.cs

@@ -0,0 +1,38 @@
+using System;
+using System.Collections.Generic;
+
+namespace CliFx
+{
+    /// <summary>
+    /// Configuration of an application.
+    /// </summary>
+    public class ApplicationConfiguration
+    {
+        /// <summary>
+        /// Command types defined in this application.
+        /// </summary>
+        public IReadOnlyList<Type> CommandTypes { get; }
+
+        /// <summary>
+        /// Whether debug mode is allowed in this application.
+        /// </summary>
+        public bool IsDebugModeAllowed { get; }
+
+        /// <summary>
+        /// Whether preview mode is allowed in this application.
+        /// </summary>
+        public bool IsPreviewModeAllowed { get; }
+
+        /// <summary>
+        /// Initializes an instance of <see cref="ApplicationConfiguration"/>.
+        /// </summary>
+        public ApplicationConfiguration(
+            IReadOnlyList<Type> commandTypes,
+            bool isDebugModeAllowed, bool isPreviewModeAllowed)
+        {
+            CommandTypes = commandTypes;
+            IsDebugModeAllowed = isDebugModeAllowed;
+            IsPreviewModeAllowed = isPreviewModeAllowed;
+        }
+    }
+}

CliFx/ApplicationMetadata.cs

@@ -1,6 +1,4 @@
-using CliFx.Internal;
-
-namespace CliFx.Models
+namespace CliFx
 {
     /// <summary>
     /// Metadata associated with an application.
@@ -25,17 +23,17 @@ namespace CliFx.Models
         /// <summary>
         /// Application description.
         /// </summary>
-        public string Description { get; }
+        public string? Description { get; }
 
         /// <summary>
         /// Initializes an instance of <see cref="ApplicationMetadata"/>.
         /// </summary>
-        public ApplicationMetadata(string title, string executableName, string versionText, string description)
+        public ApplicationMetadata(string title, string executableName, string versionText, string? description)
         {
-            Title = title.GuardNotNull(nameof(title));
-            ExecutableName = executableName.GuardNotNull(nameof(executableName));
-            VersionText = versionText.GuardNotNull(nameof(versionText));
-            Description = description; // can be null
+            Title = title;
+            ExecutableName = executableName;
+            VersionText = versionText;
+            Description = description;
         }
     }
 }

CliFx/Attributes/CommandAttribute.cs

@@ -10,27 +10,29 @@ namespace CliFx.Attributes
     {
         /// <summary>
         /// Command name.
+        /// If the name is not set, the command is treated as a default command, i.e. the one that gets executed when the user
+        /// does not specify a command name in the arguments.
+        /// All commands in an application must have different names. Likewise, only one command without a name is allowed.
         /// </summary>
-        public string Name { get; }
+        public string? Name { get; }
 
         /// <summary>
         /// Command description, which is used in help text.
         /// </summary>
-        public string Description { get; set; }
+        public string? Description { get; set; }
 
         /// <summary>
         /// Initializes an instance of <see cref="CommandAttribute"/>.
         /// </summary>
         public CommandAttribute(string name)
         {
-            Name = name; // can be null
+            Name = name;
         }
 
         /// <summary>
         /// Initializes an instance of <see cref="CommandAttribute"/>.
         /// </summary>
         public CommandAttribute()
-            : this(null)
         {
         }
     }

CliFx/Attributes/CommandOptionAttribute.cs

@@ -10,11 +10,15 @@ namespace CliFx.Attributes
     {
         /// <summary>
         /// Option name.
+        /// Either <see cref="Name"/> or <see cref="ShortName"/> must be set.
+        /// All options in a command must have different names (comparison is not case-sensitive).
         /// </summary>
-        public string Name { get; }
+        public string? Name { get; }
 
         /// <summary>
         /// Option short name.
+        /// Either <see cref="Name"/> or <see cref="ShortName"/> must be set.
+        /// All options in a command must have different short names (comparison is case-sensitive).
         /// </summary>
         public char? ShortName { get; }
 
@@ -26,15 +30,20 @@ namespace CliFx.Attributes
         /// <summary>
         /// Option description, which is used in help text.
         /// </summary>
-        public string Description { get; set; }
+        public string? Description { get; set; }
+
+        /// <summary>
+        /// Environment variable that will be used as fallback if no option value is specified.
+        /// </summary>
+        public string? EnvironmentVariableName { get; set; }
 
         /// <summary>
         /// Initializes an instance of <see cref="CommandOptionAttribute"/>.
         /// </summary>
-        public CommandOptionAttribute(string name, char? shortName)
+        private CommandOptionAttribute(string? name, char? shortName)
         {
-            Name = name; // can be null
-            ShortName = shortName; // can be null
+            Name = name;
+            ShortName = shortName;
         }
 
         /// <summary>
@@ -57,7 +66,7 @@ namespace CliFx.Attributes
         /// Initializes an instance of <see cref="CommandOptionAttribute"/>.
         /// </summary>
         public CommandOptionAttribute(char shortName)
-            : this(null, shortName)
+            : this(null, (char?) shortName)
         {
         }
     }

CliFx/Attributes/CommandParameterAttribute.cs

@@ -0,0 +1,37 @@
+using System;
+
+namespace CliFx.Attributes
+{
+    /// <summary>
+    /// Annotates a property that defines a command parameter.
+    /// </summary>
+    [AttributeUsage(AttributeTargets.Property)]
+    public class CommandParameterAttribute : Attribute
+    {
+        /// <summary>
+        /// Order of this parameter compared to other parameters.
+        /// All parameters in a command must have different order.
+        /// Parameter whose type is a non-scalar (e.g. array), must be the last in order and only one such parameter is allowed.
+        /// </summary>
+        public int Order { get; }
+
+        /// <summary>
+        /// Parameter name, which is only used in help text.
+        /// If this isn't specified, property name is used instead.
+        /// </summary>
+        public string? Name { get; set; }
+
+        /// <summary>
+        /// Parameter description, which is used in help text.
+        /// </summary>
+        public string? Description { get; set; }
+
+        /// <summary>
+        /// Initializes an instance of <see cref="CommandParameterAttribute"/>.
+        /// </summary>
+        public CommandParameterAttribute(int order)
+        {
+            Order = order;
+        }
+    }
+}

CliFx/CliApplication.Help.cs

@@ -0,0 +1,324 @@
+using System;
+using System.Linq;
+using CliFx.Domain;
+using CliFx.Internal;
+
+namespace CliFx
+{
+    public partial class CliApplication
+    {
+        private void RenderHelp(ApplicationSchema applicationSchema, CommandSchema command)
+        {
+            var column = 0;
+            var row = 0;
+
+            var childCommands = applicationSchema.GetChildCommands(command.Name);
+
+            bool IsEmpty() => column == 0 && row == 0;
+
+            void Render(string text)
+            {
+                _console.Output.Write(text);
+
+                column += text.Length;
+            }
+
+            void RenderNewLine()
+            {
+                _console.Output.WriteLine();
+
+                column = 0;
+                row++;
+            }
+
+            void RenderMargin(int lines = 1)
+            {
+                if (!IsEmpty())
+                {
+                    for (var i = 0; i < lines; i++)
+                        RenderNewLine();
+                }
+            }
+
+            void RenderIndent(int spaces = 2)
+            {
+                Render(' '.Repeat(spaces));
+            }
+
+            void RenderColumnIndent(int spaces = 20, int margin = 2)
+            {
+                if (column + margin < spaces)
+                {
+                    RenderIndent(spaces - column);
+                }
+                else
+                {
+                    Render(" ");
+                }
+            }
+
+            void RenderWithColor(string text, ConsoleColor foregroundColor)
+            {
+                _console.WithForegroundColor(foregroundColor, () => Render(text));
+            }
+
+            void RenderHeader(string text)
+            {
+                RenderWithColor(text, ConsoleColor.Magenta);
+                RenderNewLine();
+            }
+
+            void RenderApplicationInfo()
+            {
+                if (!command.IsDefault)
+                    return;
+
+                // Title and version
+                RenderWithColor(_metadata.Title, ConsoleColor.Yellow);
+                Render(" ");
+                RenderWithColor(_metadata.VersionText, ConsoleColor.Yellow);
+                RenderNewLine();
+
+                // Description
+                if (!string.IsNullOrWhiteSpace(_metadata.Description))
+                {
+                    Render(_metadata.Description);
+                    RenderNewLine();
+                }
+            }
+
+            void RenderDescription()
+            {
+                if (string.IsNullOrWhiteSpace(command.Description))
+                    return;
+
+                RenderMargin();
+                RenderHeader("Description");
+
+                RenderIndent();
+                Render(command.Description);
+                RenderNewLine();
+            }
+
+            void RenderUsage()
+            {
+                RenderMargin();
+                RenderHeader("Usage");
+
+                // Exe name
+                RenderIndent();
+                Render(_metadata.ExecutableName);
+
+                // Command name
+                if (!string.IsNullOrWhiteSpace(command.Name))
+                {
+                    Render(" ");
+                    RenderWithColor(command.Name, ConsoleColor.Cyan);
+                }
+
+                // Child command placeholder
+                if (childCommands.Any())
+                {
+                    Render(" ");
+                    RenderWithColor("[command]", ConsoleColor.Cyan);
+                }
+
+                // Parameters
+                foreach (var parameter in command.Parameters)
+                {
+                    Render(" ");
+                    Render(parameter.IsScalar
+                        ? $"<{parameter.DisplayName}>"
+                        : $"<{parameter.DisplayName}...>");
+                }
+
+                // Required options
+                var requiredOptionSchemas = command.Options
+                    .Where(o => o.IsRequired)
+                    .ToArray();
+
+                foreach (var option in requiredOptionSchemas)
+                {
+                    Render(" ");
+                    if (!string.IsNullOrWhiteSpace(option.Name))
+                    {
+                        RenderWithColor($"--{option.Name}", ConsoleColor.White);
+                        Render(" ");
+                        Render(option.IsScalar
+                            ? "<value>"
+                            : "<values...>");
+                    }
+                    else
+                    {
+                        RenderWithColor($"-{option.ShortName}", ConsoleColor.White);
+                        Render(" ");
+                        Render(option.IsScalar
+                            ? "<value>"
+                            : "<values...>");
+                    }
+                }
+
+                // Options placeholder
+                if (command.Options.Count != requiredOptionSchemas.Length)
+                {
+                    Render(" ");
+                    RenderWithColor("[options]", ConsoleColor.White);
+                }
+
+                RenderNewLine();
+            }
+
+            void RenderParameters()
+            {
+                if (!command.Parameters.Any())
+                    return;
+
+                RenderMargin();
+                RenderHeader("Parameters");
+
+                var parameters = command.Parameters
+                    .OrderBy(p => p.Order)
+                    .ToArray();
+
+                foreach (var parameter in parameters)
+                {
+                    RenderWithColor("* ", ConsoleColor.Red);
+                    RenderWithColor($"{parameter.DisplayName}", ConsoleColor.White);
+
+                    RenderColumnIndent();
+
+                    // Description
+                    if (!string.IsNullOrWhiteSpace(parameter.Description))
+                    {
+                        Render(parameter.Description);
+                    }
+
+                    RenderNewLine();
+                }
+            }
+
+            void RenderOptions()
+            {
+                RenderMargin();
+                RenderHeader("Options");
+
+                var options = command.Options
+                    .OrderByDescending(o => o.IsRequired)
+                    .ToList();
+
+                // Add built-in options
+                options.Add(CommandOptionSchema.HelpOption);
+                if (command.IsDefault)
+                    options.Add(CommandOptionSchema.VersionOption);
+
+                foreach (var option in options)
+                {
+                    if (option.IsRequired)
+                    {
+                        RenderWithColor("* ", ConsoleColor.Red);
+                    }
+                    else
+                    {
+                        RenderIndent();
+                    }
+
+                    // Short name
+                    if (option.ShortName != null)
+                    {
+                        RenderWithColor($"-{option.ShortName}", ConsoleColor.White);
+                    }
+
+                    // Delimiter
+                    if (!string.IsNullOrWhiteSpace(option.Name) && option.ShortName != null)
+                    {
+                        Render("|");
+                    }
+
+                    // Name
+                    if (!string.IsNullOrWhiteSpace(option.Name))
+                    {
+                        RenderWithColor($"--{option.Name}", ConsoleColor.White);
+                    }
+
+                    RenderColumnIndent();
+
+                    // Description
+                    if (!string.IsNullOrWhiteSpace(option.Description))
+                    {
+                        Render(option.Description);
+                        Render(" ");
+                    }
+
+                    // Environment variable
+                    if (!string.IsNullOrWhiteSpace(option.EnvironmentVariableName))
+                    {
+                        Render($"(Environment variable: {option.EnvironmentVariableName}).");
+                        Render(" ");
+                    }
+
+                    RenderNewLine();
+                }
+            }
+
+            void RenderChildCommands()
+            {
+                if (!childCommands.Any())
+                    return;
+
+                RenderMargin();
+                RenderHeader("Commands");
+
+                foreach (var childCommand in childCommands)
+                {
+                    var relativeCommandName =
+                        string.IsNullOrWhiteSpace(childCommand.Name) || string.IsNullOrWhiteSpace(command.Name)
+                            ? childCommand.Name
+                            : childCommand.Name.Substring(command.Name.Length + 1);
+
+                    // Name
+                    RenderIndent();
+                    RenderWithColor(relativeCommandName, ConsoleColor.Cyan);
+
+                    // Description
+                    if (!string.IsNullOrWhiteSpace(childCommand.Description))
+                    {
+                        RenderColumnIndent();
+                        Render(childCommand.Description);
+                    }
+
+                    RenderNewLine();
+                }
+
+                RenderMargin();
+
+                // Child command help tip
+                Render("You can run `");
+                Render(_metadata.ExecutableName);
+
+                if (!string.IsNullOrWhiteSpace(command.Name))
+                {
+                    Render(" ");
+                    RenderWithColor(command.Name, ConsoleColor.Cyan);
+                }
+
+                Render(" ");
+                RenderWithColor("[command]", ConsoleColor.Cyan);
+
+                Render(" ");
+                RenderWithColor("--help", ConsoleColor.White);
+
+                Render("` to show help on a specific command.");
+
+                RenderNewLine();
+            }
+
+            _console.ResetColor();
+            RenderApplicationInfo();
+            RenderDescription();
+            RenderUsage();
+            RenderParameters();
+            RenderOptions();
+            RenderChildCommands();
+        }
+    }
+}

CliFx/CliApplication.cs

@@ -1,144 +1,205 @@
 using System;
+using System.Collections;
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.Linq;
 using System.Threading.Tasks;
+using CliFx.Domain;
 using CliFx.Exceptions;
-using CliFx.Internal;
-using CliFx.Models;
-using CliFx.Services;
 
 namespace CliFx
 {
     /// <summary>
-    /// Default implementation of <see cref="ICliApplication"/>.
+    /// Command line application facade.
     /// </summary>
-    public class CliApplication : ICliApplication
+    public partial class CliApplication
     {
         private readonly ApplicationMetadata _metadata;
         private readonly ApplicationConfiguration _configuration;
-
         private readonly IConsole _console;
-        private readonly ICommandInputParser _commandInputParser;
-        private readonly ICommandSchemaResolver _commandSchemaResolver;
-        private readonly ICommandFactory _commandFactory;
-        private readonly ICommandInitializer _commandInitializer;
-        private readonly IHelpTextRenderer _helpTextRenderer;
+        private readonly ITypeActivator _typeActivator;
 
         /// <summary>
         /// Initializes an instance of <see cref="CliApplication"/>.
         /// </summary>
-        public CliApplication(ApplicationMetadata metadata, ApplicationConfiguration configuration,
-            IConsole console, ICommandInputParser commandInputParser, ICommandSchemaResolver commandSchemaResolver,
-            ICommandFactory commandFactory, ICommandInitializer commandInitializer, IHelpTextRenderer helpTextRenderer)
+        public CliApplication(
+            ApplicationMetadata metadata, ApplicationConfiguration configuration,
+            IConsole console, ITypeActivator typeActivator)
         {
-            _metadata = metadata.GuardNotNull(nameof(metadata));
-            _configuration = configuration.GuardNotNull(nameof(configuration));
-
-            _console = console.GuardNotNull(nameof(console));
-            _commandInputParser = commandInputParser.GuardNotNull(nameof(commandInputParser));
-            _commandSchemaResolver = commandSchemaResolver.GuardNotNull(nameof(commandSchemaResolver));
-            _commandFactory = commandFactory.GuardNotNull(nameof(commandFactory));
-            _commandInitializer = commandInitializer.GuardNotNull(nameof(commandInitializer));
-            _helpTextRenderer = helpTextRenderer.GuardNotNull(nameof(helpTextRenderer));
+            _metadata = metadata;
+            _configuration = configuration;
+            _console = console;
+            _typeActivator = typeActivator;
         }
 
-        /// <inheritdoc />
-        public async Task<int> RunAsync(IReadOnlyList<string> commandLineArguments)
+        private async ValueTask<int?> HandleDebugDirectiveAsync(CommandLineInput commandLineInput)
         {
-            commandLineArguments.GuardNotNull(nameof(commandLineArguments));
+            var isDebugMode = _configuration.IsDebugModeAllowed && commandLineInput.IsDebugDirectiveSpecified;
+            if (!isDebugMode)
+                return null;
 
-            try
-            {
-                // Get schemas for all available command types
-                var availableCommandSchemas = _commandSchemaResolver.GetCommandSchemas(_configuration.CommandTypes);
+            _console.WithForegroundColor(ConsoleColor.Green, () =>
+                _console.Output.WriteLine($"Attach debugger to PID {Process.GetCurrentProcess().Id} to continue."));
 
-                // Parse command input from arguments
-                var commandInput = _commandInputParser.ParseCommandInput(commandLineArguments);
+            while (!Debugger.IsAttached)
+                await Task.Delay(100);
 
-                // Find command schema matching the name specified in the input
-                var targetCommandSchema = availableCommandSchemas.FindByName(commandInput.CommandName);
-
-                // Handle cases where requested command is not defined
-                if (targetCommandSchema == null)
-                {
-                    var isError = false;
-
-                    // If specified a command - show error
-                    if (commandInput.IsCommandSpecified())
-                    {
-                        isError = true;
-
-                        _console.WithForegroundColor(ConsoleColor.Red,
-                            () => _console.Error.WriteLine($"Specified command [{commandInput.CommandName}] is not defined."));
+            return null;
         }
 
-                    // Get parent command schema
-                    var parentCommandSchema = availableCommandSchemas.FindParent(commandInput.CommandName);
-
-                    // Show help for parent command if it's defined
-                    if (parentCommandSchema != null)
+        private int? HandlePreviewDirective(ApplicationSchema applicationSchema, CommandLineInput commandLineInput)
         {
-                        var helpTextSource = new HelpTextSource(_metadata, availableCommandSchemas, parentCommandSchema);
-                        _helpTextRenderer.RenderHelpText(_console, helpTextSource);
-                    }
-                    // Otherwise show help for a stub default command
-                    else
-                    {
-                        var helpTextSource = new HelpTextSource(_metadata,
-                            availableCommandSchemas.Concat(CommandSchema.StubDefaultCommand).ToArray(),
-                            CommandSchema.StubDefaultCommand);
+            var isPreviewMode = _configuration.IsPreviewModeAllowed && commandLineInput.IsPreviewDirectiveSpecified;
+            if (!isPreviewMode)
+                return null;
 
-                        _helpTextRenderer.RenderHelpText(_console, helpTextSource);
+            var commandSchema = applicationSchema.TryFindCommand(commandLineInput, out var argumentOffset);
+
+            _console.Output.WriteLine("Parser preview:");
+
+            // Command name
+            if (commandSchema != null && argumentOffset > 0)
+            {
+                _console.WithForegroundColor(ConsoleColor.Cyan, () =>
+                    _console.Output.Write(commandSchema.Name));
+
+                _console.Output.Write(' ');
             }
 
-                    return isError ? -1 : 0;
+            // Parameters
+            foreach (var parameter in commandLineInput.Arguments.Skip(argumentOffset))
+            {
+                _console.Output.Write('<');
+
+                _console.WithForegroundColor(ConsoleColor.White, () =>
+                    _console.Output.Write(parameter));
+
+                _console.Output.Write('>');
+                _console.Output.Write(' ');
             }
 
-                // Show version if it was requested without specifying a command
-                if (commandInput.IsVersionRequested() && !commandInput.IsCommandSpecified())
+            // Options
+            foreach (var option in commandLineInput.Options)
             {
+                _console.Output.Write('[');
+
+                _console.WithForegroundColor(ConsoleColor.White, () =>
+                    _console.Output.Write(option));
+
+                _console.Output.Write(']');
+                _console.Output.Write(' ');
+            }
+
+            _console.Output.WriteLine();
+
+            return 0;
+        }
+
+        private int? HandleVersionOption(CommandLineInput commandLineInput)
+        {
+            // Version option is available only on the default command (i.e. when arguments are not specified)
+            var shouldRenderVersion = !commandLineInput.Arguments.Any() && commandLineInput.IsVersionOptionSpecified;
+            if (!shouldRenderVersion)
+                return null;
+
             _console.Output.WriteLine(_metadata.VersionText);
 
             return 0;
         }
 
-                // Show help if it was requested
-                if (commandInput.IsHelpRequested())
+        private int? HandleHelpOption(ApplicationSchema applicationSchema, CommandLineInput commandLineInput)
         {
-                    var helpTextSource = new HelpTextSource(_metadata, availableCommandSchemas, targetCommandSchema);
-                    _helpTextRenderer.RenderHelpText(_console, helpTextSource);
+            // Help is rendered either when it's requested or when the user provides no arguments and there is no default command
+            var shouldRenderHelp =
+                commandLineInput.IsHelpOptionSpecified ||
+                !applicationSchema.Commands.Any(c => c.IsDefault) && !commandLineInput.Arguments.Any() && !commandLineInput.Options.Any();
+
+            if (!shouldRenderHelp)
+                return null;
+
+            // Get the command schema that matches the input or use a dummy default command as a fallback
+            var commandSchema =
+                applicationSchema.TryFindCommand(commandLineInput) ??
+                CommandSchema.StubDefaultCommand;
+
+            RenderHelp(applicationSchema, commandSchema);
 
             return 0;
         }
 
-                // Create an instance of the command
-                var command = _commandFactory.CreateCommand(targetCommandSchema);
-
-                // Populate command with options according to its schema
-                _commandInitializer.InitializeCommand(command, targetCommandSchema, commandInput);
-
-                // Execute command
-                await command.ExecuteAsync(_console);
+        private async ValueTask<int> HandleCommandExecutionAsync(
+            ApplicationSchema applicationSchema,
+            CommandLineInput commandLineInput,
+            IReadOnlyDictionary<string, string> environmentVariables)
+        {
+            await applicationSchema
+                .InitializeEntryPoint(commandLineInput, environmentVariables, _typeActivator)
+                .ExecuteAsync(_console);
 
             return 0;
         }
+
+        /// <summary>
+        /// Runs the application with specified command line arguments and environment variables, and returns the exit code.
+        /// </summary>
+        public async ValueTask<int> RunAsync(
+            IReadOnlyList<string> commandLineArguments,
+            IReadOnlyDictionary<string, string> environmentVariables)
+        {
+            try
+            {
+                var applicationSchema = ApplicationSchema.Resolve(_configuration.CommandTypes);
+                var commandLineInput = CommandLineInput.Parse(commandLineArguments);
+
+                return
+                    await HandleDebugDirectiveAsync(commandLineInput) ??
+                    HandlePreviewDirective(applicationSchema, commandLineInput) ??
+                    HandleVersionOption(commandLineInput) ??
+                    HandleHelpOption(applicationSchema, commandLineInput) ??
+                    await HandleCommandExecutionAsync(applicationSchema, commandLineInput, environmentVariables);
+            }
             catch (Exception ex)
             {
                 // We want to catch exceptions in order to print errors and return correct exit codes.
-                // Also, by doing this we get rid of the annoying Windows troubleshooting dialog that shows up on unhandled exceptions.
+                // Doing this also gets rid of the annoying Windows troubleshooting dialog that shows up on unhandled exceptions.
 
-                // In case we catch a CliFx-specific exception, we want to just show the error message, not the stack trace.
-                // Stack trace isn't very useful to the user if the exception is not really coming from their code.
+                // Prefer showing message without stack trace on exceptions coming from CliFx or on CommandException
+                var errorMessage = !string.IsNullOrWhiteSpace(ex.Message) && (ex is CliFxException || ex is CommandException)
+                    ? ex.Message
+                    : ex.ToString();
 
-                // CommandException is the same, but it also lets users specify exit code so we want to return that instead of default.
+                _console.WithForegroundColor(ConsoleColor.Red, () => _console.Error.WriteLine(errorMessage));
 
-                var message = ex is CliFxException && !ex.Message.IsNullOrWhiteSpace() ? ex.Message : ex.ToString();
-                var exitCode = ex is CommandException commandEx ? commandEx.ExitCode : ex.HResult;
+                return ex is CommandException commandException
+                    ? commandException.ExitCode
+                    : ex.HResult;
+            }
+        }
 
-                _console.WithForegroundColor(ConsoleColor.Red, () => _console.Error.WriteLine(message));
+        /// <summary>
+        /// Runs the application with specified command line arguments and returns the exit code.
+        /// Environment variables are retrieved automatically.
+        /// </summary>
+        public async ValueTask<int> RunAsync(IReadOnlyList<string> commandLineArguments)
+        {
+            var environmentVariables = Environment.GetEnvironmentVariables()
+                .Cast<DictionaryEntry>()
+                .ToDictionary(e => (string) e.Key, e => (string) e.Value, StringComparer.OrdinalIgnoreCase);
 
-                return exitCode;
-            }
+            return await RunAsync(commandLineArguments, environmentVariables);
+        }
+
+        /// <summary>
+        /// Runs the application and returns the exit code.
+        /// Command line arguments and environment variables are retrieved automatically.
+        /// </summary>
+        public async ValueTask<int> RunAsync()
+        {
+            var commandLineArguments = Environment.GetCommandLineArgs()
+                .Skip(1)
+                .ToArray();
+
+            return await RunAsync(commandLineArguments);
         }
     }
 }

CliFx/CliApplicationBuilder.cs

@@ -3,155 +3,171 @@ using System.Collections.Generic;
 using System.IO;
 using System.Linq;
 using System.Reflection;
-using CliFx.Internal;
-using CliFx.Models;
-using CliFx.Services;
+using CliFx.Domain;
 
 namespace CliFx
 {
     /// <summary>
-    /// Default implementation of <see cref="ICliApplicationBuilder"/>.
+    /// Builds an instance of <see cref="CliApplication"/>.
     /// </summary>
-    public partial class CliApplicationBuilder : ICliApplicationBuilder
+    public partial class CliApplicationBuilder
     {
         private readonly HashSet<Type> _commandTypes = new HashSet<Type>();
 
-        private string _title;
-        private string _executableName;
-        private string _versionText;
-        private string _description;
-        private IConsole _console;
-        private ICommandFactory _commandFactory;
+        private bool _isDebugModeAllowed = true;
+        private bool _isPreviewModeAllowed = true;
+        private string? _title;
+        private string? _executableName;
+        private string? _versionText;
+        private string? _description;
+        private IConsole? _console;
+        private ITypeActivator? _typeActivator;
 
-        /// <inheritdoc />
-        public ICliApplicationBuilder AddCommand(Type commandType)
+        /// <summary>
+        /// Adds a command of specified type to the application.
+        /// </summary>
+        public CliApplicationBuilder AddCommand(Type commandType)
         {
-            commandType.GuardNotNull(nameof(commandType));
-
             _commandTypes.Add(commandType);
 
             return this;
         }
 
-        /// <inheritdoc />
-        public ICliApplicationBuilder AddCommandsFrom(Assembly commandAssembly)
+        /// <summary>
+        /// Adds multiple commands to the application.
+        /// </summary>
+        public CliApplicationBuilder AddCommands(IEnumerable<Type> commandTypes)
         {
-            commandAssembly.GuardNotNull(nameof(commandAssembly));
-
-            var commandTypes = commandAssembly.ExportedTypes.Where(t => t.Implements(typeof(ICommand)));
-
             foreach (var commandType in commandTypes)
                 AddCommand(commandType);
 
             return this;
         }
 
-        /// <inheritdoc />
-        public ICliApplicationBuilder UseTitle(string title)
+        /// <summary>
+        /// Adds commands from the specified assembly to the application.
+        /// Only the public types are added.
+        /// </summary>
+        public CliApplicationBuilder AddCommandsFrom(Assembly commandAssembly)
         {
-            _title = title.GuardNotNull(nameof(title));
+            foreach (var commandType in commandAssembly.ExportedTypes.Where(CommandSchema.IsCommandType))
+                AddCommand(commandType);
+
             return this;
         }
 
-        /// <inheritdoc />
-        public ICliApplicationBuilder UseExecutableName(string executableName)
+        /// <summary>
+        /// Adds commands from the specified assemblies to the application.
+        /// Only the public types are added.
+        /// </summary>
+        public CliApplicationBuilder AddCommandsFrom(IEnumerable<Assembly> commandAssemblies)
         {
-            _executableName = executableName.GuardNotNull(nameof(executableName));
+            foreach (var commandAssembly in commandAssemblies)
+                AddCommandsFrom(commandAssembly);
+
             return this;
         }
 
-        /// <inheritdoc />
-        public ICliApplicationBuilder UseVersionText(string versionText)
+        /// <summary>
+        /// Adds commands from the calling assembly to the application.
+        /// Only the public types are added.
+        /// </summary>
+        public CliApplicationBuilder AddCommandsFromThisAssembly() => AddCommandsFrom(Assembly.GetCallingAssembly());
+
+        /// <summary>
+        /// Specifies whether debug mode (enabled with [debug] directive) is allowed in the application.
+        /// </summary>
+        public CliApplicationBuilder AllowDebugMode(bool isAllowed = true)
         {
-            _versionText = versionText.GuardNotNull(nameof(versionText));
+            _isDebugModeAllowed = isAllowed;
             return this;
         }
 
-        /// <inheritdoc />
-        public ICliApplicationBuilder UseDescription(string description)
+        /// <summary>
+        /// Specifies whether preview mode (enabled with [preview] directive) is allowed in the application.
+        /// </summary>
+        public CliApplicationBuilder AllowPreviewMode(bool isAllowed = true)
         {
-            _description = description; // can be null
+            _isPreviewModeAllowed = isAllowed;
             return this;
         }
 
-        /// <inheritdoc />
-        public ICliApplicationBuilder UseConsole(IConsole console)
+        /// <summary>
+        /// Sets application title, which appears in the help text.
+        /// </summary>
+        public CliApplicationBuilder UseTitle(string title)
         {
-            _console = console.GuardNotNull(nameof(console));
+            _title = title;
             return this;
         }
 
-        /// <inheritdoc />
-        public ICliApplicationBuilder UseCommandFactory(ICommandFactory factory)
+        /// <summary>
+        /// Sets application executable name, which appears in the help text.
+        /// </summary>
+        public CliApplicationBuilder UseExecutableName(string executableName)
         {
-            _commandFactory = factory.GuardNotNull(nameof(factory));
+            _executableName = executableName;
             return this;
         }
 
-        private void SetFallbackValues()
+        /// <summary>
+        /// Sets application version text, which appears in the help text and when the user requests version information.
+        /// </summary>
+        public CliApplicationBuilder UseVersionText(string versionText)
         {
-            if (_title.IsNullOrWhiteSpace())
-            {
-                // Entry assembly is null in tests
-                UseTitle(EntryAssembly?.GetName().Name ?? "App");
+            _versionText = versionText;
+            return this;
         }
 
-            if (_executableName.IsNullOrWhiteSpace())
+        /// <summary>
+        /// Sets application description, which appears in the help text.
+        /// </summary>
+        public CliApplicationBuilder UseDescription(string? description)
         {
-                // Entry assembly is null in tests
-                var entryAssemblyLocation = EntryAssembly?.Location;
-
-                // Set different executable name depending on location
-                if (!entryAssemblyLocation.IsNullOrWhiteSpace())
-                {
-                    // Prepend 'dotnet' to assembly file name if the entry assembly is a dll file (extension needs to be kept)
-                    if (string.Equals(Path.GetExtension(entryAssemblyLocation), ".dll", StringComparison.OrdinalIgnoreCase))
-                    {
-                        UseExecutableName("dotnet " + Path.GetFileName(entryAssemblyLocation));
-                    }
-                    // Otherwise just use assembly file name without extension
-                    else
-                    {
-                        UseExecutableName(Path.GetFileNameWithoutExtension(entryAssemblyLocation));
-                    }
-                }
-                // If location is null then just use a stub
-                else
-                {
-                    UseExecutableName("app");
-                }
+            _description = description;
+            return this;
         }
 
-            if (_versionText.IsNullOrWhiteSpace())
+        /// <summary>
+        /// Configures the application to use the specified implementation of <see cref="IConsole"/>.
+        /// </summary>
+        public CliApplicationBuilder UseConsole(IConsole console)
         {
-                // Entry assembly is null in tests
-                UseVersionText(EntryAssembly?.GetName().Version.ToString() ?? "1.0");
+            _console = console;
+            return this;
         }
 
-            if (_console == null)
+        /// <summary>
+        /// Configures the application to use the specified implementation of <see cref="ITypeActivator"/>.
+        /// </summary>
+        public CliApplicationBuilder UseTypeActivator(ITypeActivator typeActivator)
         {
-                UseConsole(new SystemConsole());
+            _typeActivator = typeActivator;
+            return this;
         }
 
-            if (_commandFactory == null)
-            {
-                UseCommandFactory(new CommandFactory());
-            }
-        }
+        /// <summary>
+        /// Configures the application to use the specified function for activating types.
+        /// </summary>
+        public CliApplicationBuilder UseTypeActivator(Func<Type, object> typeActivator) =>
+            UseTypeActivator(new DelegateTypeActivator(typeActivator));
 
-        /// <inheritdoc />
-        public ICliApplication Build()
+        /// <summary>
+        /// Creates an instance of <see cref="CliApplication"/> using configured parameters.
+        /// Default values are used in place of parameters that were not specified.
+        /// </summary>
+        public CliApplication Build()
         {
-            // Use defaults for required parameters that were not configured
-            SetFallbackValues();
+            _title ??= GetDefaultTitle() ?? "App";
+            _executableName ??= GetDefaultExecutableName() ?? "app";
+            _versionText ??= GetDefaultVersionText() ?? "v1.0";
+            _console ??= new SystemConsole();
+            _typeActivator ??= new DefaultTypeActivator();
 
-            // Project parameters to expected types
             var metadata = new ApplicationMetadata(_title, _executableName, _versionText, _description);
-            var configuration = new ApplicationConfiguration(_commandTypes.ToArray());
+            var configuration = new ApplicationConfiguration(_commandTypes.ToArray(), _isDebugModeAllowed, _isPreviewModeAllowed);
 
-            return new CliApplication(metadata, configuration,
-                _console, new CommandInputParser(), new CommandSchemaResolver(),
-                _commandFactory, new CommandInitializer(), new HelpTextRenderer());
+            return new CliApplication(metadata, configuration, _console, _typeActivator);
         }
     }
 
@@ -159,6 +175,28 @@ namespace CliFx
     {
         private static readonly Lazy<Assembly> LazyEntryAssembly = new Lazy<Assembly>(Assembly.GetEntryAssembly);
 
+        // Entry assembly is null in tests
         private static Assembly EntryAssembly => LazyEntryAssembly.Value;
+
+        private static string? GetDefaultTitle() => EntryAssembly?.GetName().Name;
+
+        private static string? GetDefaultExecutableName()
+        {
+            var entryAssemblyLocation = EntryAssembly?.Location;
+
+            // If it's a .dll assembly, prepend 'dotnet' and keep the file extension
+            if (string.Equals(Path.GetExtension(entryAssemblyLocation), ".dll", StringComparison.OrdinalIgnoreCase))
+            {
+                return "dotnet " + Path.GetFileName(entryAssemblyLocation);
+            }
+
+            // Otherwise just use assembly file name without extension
+            return Path.GetFileNameWithoutExtension(entryAssemblyLocation);
+        }
+
+        private static string? GetDefaultVersionText() =>
+            EntryAssembly != null
+                ? $"v{EntryAssembly.GetName().Version}"
+                : null;
     }
 }

CliFx/CliFx.csproj

@@ -1,23 +1,41 @@
 <Project Sdk="Microsoft.NET.Sdk">
+  <Import Project="../CliFx.props" />
 
   <PropertyGroup>
-    <TargetFrameworks>net45;netstandard2.0</TargetFrameworks>
-    <LangVersion>latest</LangVersion>
-    <Version>0.0.2</Version>
-    <Company>Tyrrrz</Company>
+    <TargetFrameworks>netstandard2.1;netstandard2.0;net45</TargetFrameworks>
     <Authors>$(Company)</Authors>
-    <Copyright>Copyright (C) Alexey Golub</Copyright>
     <Description>Declarative framework for CLI applications</Description>
     <PackageTags>command line executable interface framework parser arguments net core</PackageTags>
     <PackageProjectUrl>https://github.com/Tyrrrz/CliFx</PackageProjectUrl>
     <PackageReleaseNotes>https://github.com/Tyrrrz/CliFx/blob/master/Changelog.md</PackageReleaseNotes>
-    <PackageIconUrl>https://raw.githubusercontent.com/Tyrrrz/CliFx/master/favicon.png</PackageIconUrl>
-    <PackageLicenseExpression>LGPL-3.0-only</PackageLicenseExpression>
-    <RepositoryUrl>https://github.com/Tyrrrz/CliFx</RepositoryUrl>
-    <RepositoryType>git</RepositoryType>
+    <PackageIcon>favicon.png</PackageIcon>
+    <PackageLicenseExpression>MIT</PackageLicenseExpression>
     <PackageRequireLicenseAcceptance>True</PackageRequireLicenseAcceptance>
-    <GeneratePackageOnBuild>True</GeneratePackageOnBuild>
-    <DocumentationFile>bin/$(Configuration)/$(TargetFramework)/$(AssemblyName).xml</DocumentationFile>
+    <GenerateDocumentationFile>True</GenerateDocumentationFile>
+    <PublishRepositoryUrl>True</PublishRepositoryUrl>
+    <EmbedUntrackedSources>True</EmbedUntrackedSources>
+    <IncludeSymbols>True</IncludeSymbols>
+    <SymbolPackageFormat>snupkg</SymbolPackageFormat>
   </PropertyGroup>
 
+  <ItemGroup>
+    <AssemblyAttribute Include="System.Runtime.CompilerServices.InternalsVisibleToAttribute">
+      <_Parameter1>$(AssemblyName).Tests</_Parameter1>
+    </AssemblyAttribute>
+  </ItemGroup>
+
+  <ItemGroup>
+    <None Include="../favicon.png" Pack="True" PackagePath="" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.NETFramework.ReferenceAssemblies" Version="1.0.0" PrivateAssets="all" />
+    <PackageReference Include="Microsoft.SourceLink.GitHub" Version="1.0.0" PrivateAssets="all" />
+    <PackageReference Include="Nullable" Version="1.2.0" PrivateAssets="all" />
+  </ItemGroup>
+
+  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0' or '$(TargetFramework)' == 'net45'">
+    <PackageReference Include="System.Threading.Tasks.Extensions" Version="4.5.3" />
+  </ItemGroup>
+
 </Project>

CliFx/DefaultTypeActivator.cs

@@ -0,0 +1,29 @@
+using System;
+using System.Text;
+using CliFx.Exceptions;
+
+namespace CliFx
+{
+    /// <summary>
+    /// Type activator that uses the <see cref="Activator"/> class to instantiate objects.
+    /// </summary>
+    public class DefaultTypeActivator : ITypeActivator
+    {
+        /// <inheritdoc />
+        public object CreateInstance(Type type)
+        {
+            try
+            {
+                return Activator.CreateInstance(type);
+            }
+            catch (Exception ex)
+            {
+                throw new CliFxException(new StringBuilder()
+                    .Append($"Failed to create an instance of {type.FullName}.").Append(" ")
+                    .AppendLine("The type must have a public parameter-less constructor in order to be instantiated by the default activator.")
+                    .Append($"To supply a custom activator (for example when using dependency injection), call {nameof(CliApplicationBuilder)}.{nameof(CliApplicationBuilder.UseTypeActivator)}(...).")
+                    .ToString(), ex);
+            }
+        }
+    }
+}

CliFx/DelegateTypeActivator.cs

@@ -0,0 +1,27 @@
+using System;
+using System.Text;
+using CliFx.Exceptions;
+
+namespace CliFx
+{
+    /// <summary>
+    /// Type activator that uses the specified delegate to instantiate objects.
+    /// </summary>
+    public class DelegateTypeActivator : ITypeActivator
+    {
+        private readonly Func<Type, object> _func;
+
+        /// <summary>
+        /// Initializes an instance of <see cref="DelegateTypeActivator"/>.
+        /// </summary>
+        public DelegateTypeActivator(Func<Type, object> func) => _func = func;
+
+        /// <inheritdoc />
+        public object CreateInstance(Type type) =>
+            _func(type) ?? throw new CliFxException(new StringBuilder()
+                .Append($"Failed to create an instance of type {type.FullName}, received <null> instead.").Append(" ")
+                .Append("Make sure that the provided type activator was configured correctly.").Append(" ")
+                .Append("If you are using a dependency container, make sure that this type is registered.")
+                .ToString());
+    }
+}