C# 测试模式
使用 xUnit、FluentAssertions 和现代测试实践为 .NET 应用程序提供的全面测试模式。
何时使用
- 为 C# 代码编写新测试
- 审查测试质量和覆盖率
- 为 .NET 项目搭建测试基础设施
- 调试不稳定或缓慢的测试
测试框架栈
| 工具 | 用途 |
|---|---|
| xUnit | 测试框架（.NET 首选） |
| FluentAssertions | 可读的断言语法 |
| NSubstitute 或 Moq | 模拟依赖项 |
| Testcontainers | 集成测试中的真实基础设施 |
| WebApplicationFactory | ASP.NET Core 集成测试 |
| Bogus | 生成逼真的测试数据 |
单元测试结构
安排-操作-断言
csharp
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"); }}使用 Theory 的参数化测试
csharp
[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" },};使用 NSubstitute 进行模拟
csharp
[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 集成测试
WebApplicationFactory 设置
csharp
public sealed class OrderApiTests : IClassFixture<WebApplicationFactory<Program>>{ private readonly HttpClient _client;
public OrderApiTests(WebApplicationFactory<Program> factory) { _client = factory.WithWebHostBuilder(builder => { builder.ConfigureServices(services => { // Replace real DB with in-memory for tests 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(); }}使用 Testcontainers 进行测试
csharp
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); }}测试组织
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测试数据构建器
csharp
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);}
// Usage in testsvar order = new OrderBuilder() .WithCustomer("cust-vip") .WithItem("SKU-PREMIUM", 3, 99.99m) .Build();常见反模式
| 反模式 | 修复方法 |
|---|---|
| 测试实现细节 | 测试行为和结果 |
| 共享的可变测试状态 | 每个测试使用新实例（xUnit 通过构造函数实现） |
在异步测试中使用 Thread.Sleep | 使用带超时的 Task.Delay 或轮询辅助方法 |
对 ToString() 输出进行断言 | 对类型化属性进行断言 |
| 每个测试一个巨型断言 | 每个测试一个逻辑断言 |
| 测试名称描述实现 | 按行为命名：Method_ExpectedResult_WhenCondition |
忽略 CancellationToken | 始终传递并验证取消 |
运行测试
bash
# Run all testsdotnet test
# Run with coveragedotnet test --collect:"XPlat Code Coverage"
# Run specific projectdotnet test tests/MyApp.UnitTests/
# Filter by test namedotnet test --filter "FullyQualifiedName~OrderService"
# Watch mode during developmentdotnet watch test --project tests/MyApp.UnitTests/
