Unit Test Generator

Overview

Unit tests for Clean Architecture handlers:

• xUnit - Test framework
• NSubstitute - Mocking library
• FluentAssertions - Readable assertions
• AAA pattern - Arrange, Act, Assert

Quick Reference

Test Project Structure

tests/
└── {name}.Application.UnitTests/
    ├── {Feature}/
    │   ├── Create{Entity}/
    │   │   ├── Create{Entity}CommandHandlerTests.cs
    │   │   └── Create{Entity}CommandValidatorTests.cs
    │   └── Get{Entity}ById/
    │       └── Get{Entity}ByIdQueryHandlerTests.cs
    ├── Abstractions/
    │   └── BaseTest.cs
    └── {name}.Application.UnitTests.csproj

Template: Test Project File

<!-- tests/{name}.Application.UnitTests/{name}.Application.UnitTests.csproj -->
<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <TargetFramework>net8.0</TargetFramework>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
    <IsPackable>false</IsPackable>
    <IsTestProject>true</IsTestProject>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="FluentAssertions" Version="6.12.0" />
    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.8.0" />
    <PackageReference Include="NSubstitute" Version="5.1.0" />
    <PackageReference Include="NSubstitute.Analyzers.CSharp" Version="1.0.16">
      <PrivateAssets>all</PrivateAssets>
      <IncludeAssets>runtime; build; native; contentfiles; analyzers</IncludeAssets>
    </PackageReference>
    <PackageReference Include="xunit" Version="2.6.2" />
    <PackageReference Include="xunit.runner.visualstudio" Version="2.5.4">
      <PrivateAssets>all</PrivateAssets>
      <IncludeAssets>runtime; build; native; contentfiles; analyzers</IncludeAssets>
    </PackageReference>
    <PackageReference Include="coverlet.collector" Version="6.0.0">
      <PrivateAssets>all</PrivateAssets>
      <IncludeAssets>runtime; build; native; contentfiles; analyzers</IncludeAssets>
    </PackageReference>
  </ItemGroup>

  <ItemGroup>
    <ProjectReference Include="..\..\src\{name}.application\{name}.application.csproj" />
    <ProjectReference Include="..\..\src\{name}.domain\{name}.domain.csproj" />
  </ItemGroup>

</Project>

Template: Base Test Class

// tests/{name}.Application.UnitTests/Abstractions/BaseTest.cs
using NSubstitute;
using {name}.domain.abstractions;

namespace {name}.Application.UnitTests.Abstractions;

public abstract class BaseTest
{
    protected static CancellationToken CancellationToken => CancellationToken.None;

    /// <summary>
    /// Creates a mock that returns the provided result
    /// </summary>
    protected static T CreateMock<T>() where T : class
    {
        return Substitute.For<T>();
    }

    /// <summary>
    /// Helper to create a successful Result
    /// </summary>
    protected static Result<T> SuccessResult<T>(T value)
    {
        return Result.Success(value);
    }

    /// <summary>
    /// Helper to create a failed Result
    /// </summary>
    protected static Result<T> FailureResult<T>(Error error)
    {
        return Result.Failure<T>(error);
    }
}

Template: Command Handler Tests

// tests/{name}.Application.UnitTests/{Feature}/Create{Entity}/Create{Entity}CommandHandlerTests.cs
using FluentAssertions;
using NSubstitute;
using {name}.application.{feature}.Create{Entity};
using {name}.domain.{aggregate};
using {name}.domain.abstractions;
using {name}.Application.UnitTests.Abstractions;

namespace {name}.Application.UnitTests.{Feature}.Create{Entity};

public sealed class Create{Entity}CommandHandlerTests : BaseTest
{
    private readonly I{Entity}Repository _{entity}Repository;
    private readonly IUnitOfWork _unitOfWork;
    private readonly Create{Entity}CommandHandler _handler;

    public Create{Entity}CommandHandlerTests()
    {
        // Arrange - Setup mocks (runs before each test)
        _{entity}Repository = CreateMock<I{Entity}Repository>();
        _unitOfWork = CreateMock<IUnitOfWork>();

        _handler = new Create{Entity}CommandHandler(
            _{entity}Repository,
            _unitOfWork);
    }

    // ═══════════════════════════════════════════════════════════════
    // SUCCESS TESTS
    // ═══════════════════════════════════════════════════════════════

    [Fact]
    public async Task Handle_Should_ReturnSuccess_When_ValidRequest()
    {
        // Arrange
        var command = new Create{Entity}Command(
            Name: "Test Entity",
            Description: "Test Description",
            OrganizationId: Guid.NewGuid());

        _{entity}Repository
            .GetByNameAsync(command.Name, CancellationToken)
            .Returns((Domain.{Aggregate}.{Entity}?)null);

        // Act
        var result = await _handler.Handle(command, CancellationToken);

        // Assert
        result.IsSuccess.Should().BeTrue();
        result.Value.Should().NotBeEmpty();
    }

    [Fact]
    public async Task Handle_Should_AddEntity_When_ValidRequest()
    {
        // Arrange
        var command = new Create{Entity}Command(
            Name: "Test Entity",
            Description: "Test Description",
            OrganizationId: Guid.NewGuid());

        _{entity}Repository
            .GetByNameAsync(command.Name, CancellationToken)
            .Returns((Domain.{Aggregate}.{Entity}?)null);

        // Act
        await _handler.Handle(command, CancellationToken);

        // Assert
        _{entity}Repository
            .Received(1)
            .Add(Arg.Is<Domain.{Aggregate}.{Entity}>(e =>
                e.Name == command.Name &&
                e.OrganizationId == command.OrganizationId));
    }

    [Fact]
    public async Task Handle_Should_CallSaveChanges_When_ValidRequest()
    {
        // Arrange
        var command = new Create{Entity}Command(
            Name: "Test Entity",
            Description: "Test Description",
            OrganizationId: Guid.NewGuid());

        _{entity}Repository
            .GetByNameAsync(command.Name, CancellationToken)
            .Returns((Domain.{Aggregate}.{Entity}?)null);

        // Act
        await _handler.Handle(command, CancellationToken);

        // Assert
        await _unitOfWork
            .Received(1)
            .SaveChangesAsync(CancellationToken);
    }

    // ═══════════════════════════════════════════════════════════════
    // FAILURE TESTS
    // ═══════════════════════════════════════════════════════════════

    [Fact]
    public async Task Handle_Should_ReturnFailure_When_NameAlreadyExists()
    {
        // Arrange
        var command = new Create{Entity}Command(
            Name: "Existing Entity",
            Description: "Test Description",
            OrganizationId: Guid.NewGuid());

        var existing{Entity} = CreateTest{Entity}(command.Name);

        _{entity}Repository
            .GetByNameAsync(command.Name, CancellationToken)
            .Returns(existing{Entity});

        // Act
        var result = await _handler.Handle(command, CancellationToken);

        // Assert
        result.IsFailure.Should().BeTrue();
        result.Error.Should().Be({Entity}Errors.NameAlreadyExists);
    }

    [Fact]
    public async Task Handle_Should_NotAddEntity_When_NameAlreadyExists()
    {
        // Arrange
        var command = new Create{Entity}Command(
            Name: "Existing Entity",
            Description: "Test Description",
            OrganizationId: Guid.NewGuid());

        var existing{Entity} = CreateTest{Entity}(command.Name);

        _{entity}Repository
            .G