$ ~/registry/skill/affaan-m-csharp-testing

SKILL

csharp-testing

Write and improve C#/.NET unit and integration tests with proven patterns.

Stars

★ 243,958

Source

GitHub

Updated

2026-08-28

// securityLow risk

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// install

Copy the install command and let the AI configure it · recommended for beginners

Please install the "csharp-testing" skill from askskill:
1. Download https://raw.githubusercontent.com/affaan-m/ECC/main/skills/csharp-testing/SKILL.md
2. Save it as ~/.claude/skills/csharp-testing/SKILL.md
3. Reload skills and tell me it's ready

// download

Download SKILL.mdInstall manifest ↗

// examples

Write unit tests for a service class

Prompt

Write xUnit unit tests for this C# OrderService using Arrange-Act-Assert and FluentAssertions. Cover both successful order placement and failure when the item list is empty.

Expected

A clear set of xUnit test cases with assertions for both success and failure scenarios.

Generate parameterized tests

Prompt

Rewrite this email validation test as an xUnit Theory using InlineData to cover valid and invalid email inputs.

Expected

A parameterized test example using Theory and InlineData.

Review test quality

Prompt

Review this .NET test suite and suggest improvements for readability, coverage, mock usage, and test organization.

Expected

A list of improvements for test structure, assertions, coverage gaps, and organization practices.

// use cases

Add tests for new C# features

Developers can use it to quickly create xUnit tests, assertion patterns, and baseline test structure for new .NET business logic. It helps standardize common testing practices.

Review test quality and coverage approach

When a team needs to assess whether existing tests are clear, complete, or maintainable, it can review test organization, parameterized tests, and mock usage.

Set up .NET integration testing

For ASP.NET Core projects or systems that depend on real infrastructure, it can guide integration test setup using tools like WebApplicationFactory and Testcontainers.

// docs

AI summary

The document outlines testing patterns for .NET applications, centered on a stack that includes xUnit, FluentAssertions, and NSubstitute or Moq. It covers Arrange-Act-Assert unit test structure, parameterized tests with Theory, and broader guidance on integration testing, test infrastructure setup, test quality review, and debugging slow or flaky tests.

Show full docs ▾

C# Testing Patterns

Comprehensive testing patterns for .NET applications using xUnit, FluentAssertions, and modern testing practices.

When to Activate

Writing new tests for C# code
Reviewing test quality and coverage
Setting up test infrastructure for .NET projects
Debugging flaky or slow tests

Test Framework Stack

Tool	Purpose
xUnit	Test framework (preferred for .NET)
FluentAssertions	Readable assertion syntax
NSubstitute or Moq	Mocking dependencies
Testcontainers	Real infrastructure in integration tests
WebApplicationFactory	ASP.NET Core integration tests
Bogus	Realistic test data generation

Unit Test Structure

Arrange-Act-Assert

public sealed class OrderServiceTests
{
    private readonly IOrderRepository _repository = Substitute.For<IOrderRepository>();
    private readonly ILogger<OrderService> _logger = Substitute.For<ILogger<OrderService>>();
    private readonly OrderService _sut;

    public OrderServiceTests()
    {
        _sut = new OrderService(_repository, _logger);
    }

    [Fact]
    public async Task PlaceOrderAsync_ReturnsSuccess_WhenRequestIsValid()
    {
        // Arrange
        var request = new CreateOrderRequest
        {
            CustomerId = "cust-123",
            Items = [new OrderItem("SKU-001", 2, 29.99m)]
        };

        // Act
        var result = await _sut.PlaceOrderAsync(request, CancellationToken.None);

        // Assert
        result.IsSuccess.Should().BeTrue();
        result.Value.Should().NotBeNull();
        result.Value!.CustomerId.Should().Be("cust-123");
    }

    [Fact]
    public async Task PlaceOrderAsync_ReturnsFailure_WhenNoItems()
    {
        // Arrange
        var request = new CreateOrderRequest
        {
            CustomerId = "cust-123",
            Items = []
        };

        // Act
        var result = await _sut.PlaceOrderAsync(request, CancellationToken.None);

        // Assert
        result.IsSuccess.Should().BeFalse();
        result.Error.Should().Contain("at least one item");
    }
}

Parameterized Tests with Theory

[Theory]
[InlineData("", false)]
[InlineData("a", false)]
[InlineData("[email protected]", false)]
[InlineData("[email protected]", true)]
[InlineData("[email protected]", true)]
public void IsValidEmail_ReturnsExpected(string email, bool expected)
{
    EmailValidator.IsValid(email).Should().Be(expected);
}

[Theory]
[MemberData(nameof(InvalidOrderCases))]
public async Task PlaceOrderAsync_RejectsInvalidOrders(CreateOrderRequest request, string expectedError)
{
    var result = await _sut.PlaceOrderAsync(request, CancellationToken.None);

    result.IsSuccess.Should().BeFalse();
    result.Error.Should().Contain(expectedError);
}

public static TheoryData<CreateOrderRequest, string> InvalidOrderCases => new()
{
    { new() { CustomerId = "", Items = [ValidItem()] }, "CustomerId" },
    { new() { CustomerId = "c1", Items = [] }, "at least one item" },
    { new() { CustomerId = "c1", Items = [new("", 1, 10m)] }, "SKU" },
};

Mocking with NSubstitute

[Fact]
public async Task GetOrderAsync_ReturnsNull_WhenNotFound()
{
    // Arrange
    var orderId = Guid.NewGuid();
    _repository.FindByIdAsync(orderId, Arg.Any<CancellationToken>())
        .Returns((Order?)null);

    // Act
    var result = await _sut.GetOrderAsync(orderId, CancellationToken.None);

    // Assert
    result.Should().BeNull();
}

[Fact]
public async Task PlaceOrderAsync_PersistsOrder()
{
    // Arrange
    var request = ValidOrderRequest();

    // Act
    await _sut.PlaceOrderAsync(request, CancellationToken.None);

    // Assert — verify the repository was called
    await _repository.Received(1).AddAsync(
        Arg.Is<Order>(o => o.CustomerId == request.CustomerId),
        Arg.Any<CancellationToken>());
}

ASP.NET Core Integration Tests

WebApplicationFactory Setup

…

View full docs ↗

// FAQ

What is this skill mainly for?

It is for C# and .NET testing practices, including xUnit, FluentAssertions, mocking, integration tests, and test organization best practices. It is suitable for writing new tests, reviewing test quality, and debugging flaky tests.

Which testing tools does it recommend?

The excerpt mentions xUnit, FluentAssertions, NSubstitute or Moq, Testcontainers, WebApplicationFactory, and Bogus. For exact configuration details, see the source repository.

Does it include integration testing guidance?

Yes. The excerpt explicitly mentions using Testcontainers for real-infrastructure integration tests and WebApplicationFactory for ASP.NET Core integration tests.

Helps developers avoid common testing anti-patterns and write more reliable tests.

obraGet→

$ loading_

Please install the "csharp-testing" skill from askskill: 1. Download https://raw.githubusercontent.com/affaan-m/ECC/main/skills/csharp-testing/SKILL.md 2. Save it as ~/.claude/skills/csharp-testing/SKILL.md 3. Reload skills and tell me it's ready

// examples

Write unit tests for a service class

Prompt

Write xUnit unit tests for this C# OrderService using Arrange-Act-Assert and FluentAssertions. Cover both successful order placement and failure when the item list is empty.

Expected

A clear set of xUnit test cases with assertions for both success and failure scenarios.

Generate parameterized tests

Prompt

Rewrite this email validation test as an xUnit Theory using InlineData to cover valid and invalid email inputs.

Expected

A parameterized test example using Theory and InlineData.

Review test quality

Prompt

Review this .NET test suite and suggest improvements for readability, coverage, mock usage, and test organization.

Expected

A list of improvements for test structure, assertions, coverage gaps, and organization practices.

// use cases

Add tests for new C# features

Developers can use it to quickly create xUnit tests, assertion patterns, and baseline test structure for new .NET business logic. It helps standardize common testing practices.

Review test quality and coverage approach

When a team needs to assess whether existing tests are clear, complete, or maintainable, it can review test organization, parameterized tests, and mock usage.

Set up .NET integration testing

For ASP.NET Core projects or systems that depend on real infrastructure, it can guide integration test setup using tools like WebApplicationFactory and Testcontainers.

// docs

AI summary

Show full docs ▾

C# Testing Patterns

Comprehensive testing patterns for .NET applications using xUnit, FluentAssertions, and modern testing practices.

When to Activate

Writing new tests for C# code
Reviewing test quality and coverage
Setting up test infrastructure for .NET projects
Debugging flaky or slow tests

Test Framework Stack

Tool	Purpose
xUnit	Test framework (preferred for .NET)
FluentAssertions	Readable assertion syntax
NSubstitute or Moq	Mocking dependencies
Testcontainers	Real infrastructure in integration tests
WebApplicationFactory	ASP.NET Core integration tests
Bogus	Realistic test data generation

Unit Test Structure

Arrange-Act-Assert

public sealed class OrderServiceTests
{
    private readonly IOrderRepository _repository = Substitute.For<IOrderRepository>();
    private readonly ILogger<OrderService> _logger = Substitute.For<ILogger<OrderService>>();
    private readonly OrderService _sut;

    public OrderServiceTests()
    {
        _sut = new OrderService(_repository, _logger);
    }

    [Fact]
    public async Task PlaceOrderAsync_ReturnsSuccess_WhenRequestIsValid()
    {
        // Arrange
        var request = new CreateOrderRequest
        {
            CustomerId = "cust-123",
            Items = [new OrderItem("SKU-001", 2, 29.99m)]
        };

        // Act
        var result = await _sut.PlaceOrderAsync(request, CancellationToken.None);

        // Assert
        result.IsSuccess.Should().BeTrue();
        result.Value.Should().NotBeNull();
        result.Value!.CustomerId.Should().Be("cust-123");
    }

    [Fact]
    public async Task PlaceOrderAsync_ReturnsFailure_WhenNoItems()
    {
        // Arrange
        var request = new CreateOrderRequest
        {
            CustomerId = "cust-123",
            Items = []
        };

        // Act
        var result = await _sut.PlaceOrderAsync(request, CancellationToken.None);

        // Assert
        result.IsSuccess.Should().BeFalse();
        result.Error.Should().Contain("at least one item");
    }
}

Parameterized Tests with Theory

[Theory]
[InlineData("", false)]
[InlineData("a", false)]
[InlineData("[email protected]", false)]
[InlineData("[email protected]", true)]
[InlineData("[email protected]", true)]
public void IsValidEmail_ReturnsExpected(string email, bool expected)
{
    EmailValidator.IsValid(email).Should().Be(expected);
}

[Theory]
[MemberData(nameof(InvalidOrderCases))]
public async Task PlaceOrderAsync_RejectsInvalidOrders(CreateOrderRequest request, string expectedError)
{
    var result = await _sut.PlaceOrderAsync(request, CancellationToken.None);

    result.IsSuccess.Should().BeFalse();
    result.Error.Should().Contain(expectedError);
}

public static TheoryData<CreateOrderRequest, string> InvalidOrderCases => new()
{
    { new() { CustomerId = "", Items = [ValidItem()] }, "CustomerId" },
    { new() { CustomerId = "c1", Items = [] }, "at least one item" },
    { new() { CustomerId = "c1", Items = [new("", 1, 10m)] }, "SKU" },
};

Mocking with NSubstitute

[Fact]
public async Task GetOrderAsync_ReturnsNull_WhenNotFound()
{
    // Arrange
    var orderId = Guid.NewGuid();
    _repository.FindByIdAsync(orderId, Arg.Any<CancellationToken>())
        .Returns((Order?)null);

    // Act
    var result = await _sut.GetOrderAsync(orderId, CancellationToken.None);

    // Assert
    result.Should().BeNull();
}

[Fact]
public async Task PlaceOrderAsync_PersistsOrder()
{
    // Arrange
    var request = ValidOrderRequest();

    // Act
    await _sut.PlaceOrderAsync(request, CancellationToken.None);

    // Assert — verify the repository was called
    await _repository.Received(1).AddAsync(
        Arg.Is<Order>(o => o.CustomerId == request.CustomerId),
        Arg.Any<CancellationToken>());
}

ASP.NET Core Integration Tests

WebApplicationFactory Setup

…

View full docs ↗

// FAQ

What is this skill mainly for?

Which testing tools does it recommend?

The excerpt mentions xUnit, FluentAssertions, NSubstitute or Moq, Testcontainers, WebApplicationFactory, and Bogus. For exact configuration details, see the source repository.

Does it include integration testing guidance?

Yes. The excerpt explicitly mentions using Testcontainers for real-infrastructure integration tests and WebApplicationFactory for ASP.NET Core integration tests.