Skill Market

csharp testing

xUnit、FluentAssertions、モッキング、統合テスト、テスト組織のベストプラクティスを使用したC#と.NETのテストパターン。

GitHub
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0 installs262.1K GitHub starsby affaan-m

Skill Introduction

Overview
xUnit、FluentAssertions、モッキング、統合テスト、テスト組織のベストプラクティスを使用したC#と.NETのテストパターン。

Core value

Turns reusable Testing know-how into an installable skill, helping users complete github, community work faster.

Target users

  • Developers, testers, and maintainers who handle Testing tasks in Focus Code.
  • Teams that already trust workflows or content from affaan-m.
  • Users who want standardized prompts, steps, or conventions instead of repeating setup work.

Best practices

  • Read the skill content first to confirm required inputs, expected outputs, and dependencies.
  • Try it on a small task before relying on it for critical work.
  • Add project-specific constraints such as coding style, target platform, test expectations, and delivery format.
  • For external sources, verify the source link, version, and recent maintenance activity.

Best use cases

  • Tasks related to github, community that need a reusable execution flow.
  • Converting a community repo, team convention, or personal workflow into day-to-day assistance.
  • Starting from a proven skill instead of writing prompts or procedures from scratch.

Limits and boundaries

  • Results depend on the quality of the original skill content and may need human correction.
  • It does not replace code review, tests, security review, or professional judgment.
  • External tools, APIs, account permissions, and local dependencies still need separate setup.

Differentiation

  • Structured around Testing, making it easier to discover and reuse than loose prompt snippets.
  • Marked as GitHub, which helps users judge trust and maintenance expectations.
  • Keeps the original source link available for repository, documentation, or discussion follow-up.
  • Tagged with github, community, so it can be filtered by concrete task intent.

Install and use

Install
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focus install csharp-testing-0ec0c3
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SKILL.md

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name: csharp-testing description: xUnit、FluentAssertions、モッキング、統合テスト、テスト組織のベストプラクティスを使用したC#と.NETのテストパターン。 origin: ECC

C#テストパターン

xUnit、FluentAssertions、最新のテストプラクティスを使用した.NETアプリケーションの包括的なテストパターン。

起動条件

  • C#コードの新しいテストを書く場合
  • テスト品質とカバレッジのレビュー
  • .NETプロジェクトのテストインフラストラクチャの設定
  • フレーキーまたは遅いテストのデバッグ

テストフレームワークスタック

ツール目的
xUnitテストフレームワーク（.NETに推奨）
FluentAssertions読みやすいアサーション構文
NSubstituteまたはMoq依存関係のモッキング
Testcontainers統合テストでの実際のインフラ
WebApplicationFactoryASP.NET Core統合テスト
Bogus現実的なテストデータ生成

ユニットテスト構造

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");
    }
}

Theoryによるパラメータ化テスト

[Theory]
[InlineData("", false)]
[InlineData("a", false)]
[InlineData("ab@c.d", false)]
[InlineData("user@example.com", true)]
[InlineData("user+tag@example.co.uk", 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" },
};

NSubstituteによるモッキング

[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 — リポジトリが呼び出されたことを検証
    await _repository.Received(1).AddAsync(
        Arg.Is<Order>(o => o.CustomerId == request.CustomerId),
        Arg.Any<CancellationToken>());
}

ASP.NET Core統合テスト

WebApplicationFactoryのセットアップ

public sealed class OrderApiTests : IClassFixture<WebApplicationFactory<Program>>
{
    private readonly HttpClient _client;

    public OrderApiTests(WebApplicationFactory<Program> factory)
    {
        _client = factory.WithWebHostBuilder(builder =>
        {
            builder.ConfigureServices(services =>
            {
                // テスト用にインメモリDBで実際のDBを置き換え
                services.RemoveAll<DbContextOptions<AppDbContext>>();
                services.AddDbContext<AppDbContext>(options =>
                    options.UseInMemoryDatabase("TestDb"));
            });
        }).CreateClient();
    }

    [Fact]
    public async Task GetOrder_Returns404_WhenNotFound()
    {
        var response = await _client.GetAsync($"/api/orders/{Guid.NewGuid()}");

        response.StatusCode.Should().Be(HttpStatusCode.NotFound);
    }

    [Fact]
    public async Task CreateOrder_Returns201_WithValidRequest()
    {
        var request = new CreateOrderRequest
        {
            CustomerId = "cust-1",
            Items = [new("SKU-001", 1, 19.99m)]
        };

        var response = await _client.PostAsJsonAsync("/api/orders", request);

        response.StatusCode.Should().Be(HttpStatusCode.Created);
        response.Headers.Location.Should().NotBeNull();
    }
}

Testcontainersによるテスト

public sealed class PostgresOrderRepositoryTests : IAsyncLifetime
{
    private readonly PostgreSqlContainer _postgres = new PostgreSqlBuilder()
        .WithImage("postgres:16-alpine")
        .Build();

    private AppDbContext _db = null!;

    public async Task InitializeAsync()
    {
        await _postgres.StartAsync();
        var options = new DbContextOptionsBuilder<AppDbContext>()
            .UseNpgsql(_postgres.GetConnectionString())
            .Options;
        _db = new AppDbContext(options);
        await _db.Database.MigrateAsync();
    }

    public async Task DisposeAsync()
    {
        await _db.DisposeAsync();
        await _postgres.DisposeAsync();
    }

    [Fact]
    public async Task AddAsync_PersistsOrder()
    {
        var repo = new SqlOrderRepository(_db);
        var order = Order.Create("cust-1", [new OrderItem("SKU-001", 2, 10m)]);

        await repo.AddAsync(order, CancellationToken.None);

        var found = await repo.FindByIdAsync(order.Id, CancellationToken.None);
        found.Should().NotBeNull();
        found!.Items.Should().HaveCount(1);
    }
}

テスト組織

tests/
  MyApp.UnitTests/
    Services/
      OrderServiceTests.cs
      PaymentServiceTests.cs
    Validators/
      EmailValidatorTests.cs
  MyApp.IntegrationTests/
    Api/
      OrderApiTests.cs
    Repositories/
      OrderRepositoryTests.cs
  MyApp.TestHelpers/
    Builders/
      OrderBuilder.cs
    Fixtures/
      DatabaseFixture.cs

テストデータビルダー

public sealed class OrderBuilder
{
    private string _customerId = "cust-default";
    private readonly List<OrderItem> _items = [new("SKU-001", 1, 10m)];

    public OrderBuilder WithCustomer(string customerId)
    {
        _customerId = customerId;
        return this;
    }

    public OrderBuilder WithItem(string sku, int quantity, decimal price)
    {
        _items.Add(new OrderItem(sku, quantity, price));
        return this;
    }

    public Order Build() => Order.Create(_customerId, _items);
}

// テストでの使用
var order = new OrderBuilder()
    .WithCustomer("cust-vip")
    .WithItem("SKU-PREMIUM", 3, 99.99m)
    .Build();

よくあるアンチパターン

アンチパターン修正方法
実装の詳細をテストする動作と結果をテストする
共有の可変テスト状態テストごとに新しいインスタンス（xUnitはコンストラクタでこれを行う）
非同期テストでのThread.Sleepタイムアウトまたはポーリングヘルパーを使用したTask.Delay
ToString()出力のアサーション型付きプロパティのアサーション
テストごとに1つの巨大なアサーションテストごとに1つの論理的なアサーション
実装を記述するテスト名動作で命名: Method_ExpectedResult_WhenCondition
CancellationTokenを無視する常に渡してキャンセルを確認する

テストの実行

# すべてのテストを実行
dotnet test

# カバレッジを付けて実行
dotnet test --collect:"XPlat Code Coverage"

# 特定のプロジェクトを実行
dotnet test tests/MyApp.UnitTests/

# テスト名でフィルタリング
dotnet test --filter "FullyQualifiedName~OrderService"

# 開発中のウォッチモード
dotnet watch test --project tests/MyApp.UnitTests/

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