dotnet-testing

.NET Testing Patterns (stack-agnostic)

Test framework: xUnit

xUnit is the primary test framework for .NET. Use NUnit or MSTest only when the project already uses them — do not introduce xUnit into a project that uses another framework.

NuGet packages for a test project

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <TargetFramework>net8.0</TargetFramework>
    <IsPackable>false</IsPackable>
    <IsTestProject>true</IsTestProject>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="xunit" Version="2.9.2" />
    <PackageReference Include="xunit.runner.visualstudio" Version="2.8.2">
      <PrivateAssets>all</PrivateAssets>
    </PackageReference>
    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.11.1" />
    <PackageReference Include="Moq" Version="4.20.72" />
    <PackageReference Include="FluentAssertions" Version="6.12.1" />
    <PackageReference Include="coverlet.collector" Version="6.0.2">
      <PrivateAssets>all</PrivateAssets>
    </PackageReference>
  </ItemGroup>
</Project>

xUnit fundamentals

using FluentAssertions;
using Moq;
using Xunit;

public class UserServiceTests
{
    private readonly Mock<IUserRepository> _repoMock;
    private readonly UserService _sut;

    public UserServiceTests()
    {
        _repoMock = new Mock<IUserRepository>(MockBehavior.Strict);
        _sut = new UserService(_repoMock.Object);
    }

    [Fact]
    public async Task RegisterAsync_WithValidData_ReturnsActiveUser()
    {
        // Arrange
        var command = new RegisterUserCommand("[email protected]", "Secret1!");
        _repoMock.Setup(r => r.ExistsByEmailAsync("[email protected]", default))
                 .ReturnsAsync(false);
        _repoMock.Setup(r => r.SaveAsync(It.IsAny<User>(), default))
                 .ReturnsAsync((User u, CancellationToken _) => u);

        // Act
        var user = await _sut.RegisterAsync(command);

        // Assert
        user.Email.Should().Be("[email protected]");
        user.IsActive.Should().BeTrue();
        _repoMock.VerifyAll();
    }

    [Fact]
    public async Task RegisterAsync_WithDuplicateEmail_ThrowsDomainException()
    {
        _repoMock.Setup(r => r.ExistsByEmailAsync(It.IsAny<string>(), default))
                 .ReturnsAsync(true);

        await _sut.Invoking(s => s.RegisterAsync(new RegisterUserCommand("[email protected]", "pass")))
                  .Should().ThrowAsync<DomainException>()
                  .WithMessage("*already registered*");
    }
}