使用 Moq 模拟惰性接口

Question

我想要模拟惰性接口，但我得到了object reference not set to an instance of an object 异常。

‌这是正在测试的课程：

public class ProductServiceService : IProductServiceService
{
    private readonly Lazy<IProductServiceRepository> _repository;
    private readonly Lazy<IProductPackageRepository> _productPackageRepository;

    public ProductServiceService(
        Lazy<IProductServiceRepository> repository,
        Lazy<IProductPackageRepository> productPackageRepository)
    {
        _repository = repository;
        _productPackageRepository = productPackageRepository;
    }

    public async Task<OperationResult> ValidateServiceAsync(ProductServiceEntity service)
    {
        var errors = new List<ValidationResult>();

        if (!await _productPackageRepository.Value.AnyAsync(p => p.Id == service.PackageId))
            errors.Add(new ValidationResult(string.Format(NameMessageResource.NotFoundError, NameMessageResource.ProductPackage)));

       .
       .
       .

        return errors.Any()
            ? OperationResult.Failed(errors.ToArray())
            : OperationResult.Success();
    }
}

这里是测试类

[Fact, Trait("Category", "Product")]
public async Task Create_Service_With_Null_Financial_ContactPerson_Should_Fail()
{
    // Arrange
    var entity = ObjectFactory.Service.CreateService(packageId: 1);

    var fakeProductServiceRepository = new Mock<Lazy<IProductServiceRepository>>();

    var repo= new Mock<IProductPackageRepository>();
    repo.Setup(repository => repository.AnyAsync(It.IsAny<Expression<Func<ProductPackageEntity, bool>>>()));
    var fakeProductPackageRepository  = new Lazy<IProductPackageRepository>(() => repo.Object);

    var sut = new ProductServiceService(fakeProductServiceRepository.Object, fakeProductPackageRepository);

    // Act
    var result = await sut.AddServiceAsync(service);

    // Assert
    Assert.False(result.Succeeded);
    Assert.Contains(result.ErrorMessages, error => error.Contains(string.Format(NameMessageResource.NotFoundError, NameMessageResource.ProductPackage)));
}

fakeProductPackageRepository 始终为空。我关注了这篇博文，但仍然收到空引用异常。

How to mock lazy initialization of objects in C# unit tests using Moq

更新： 这是一个指示fakeProductPackageRepository 为空的屏幕。

Answer 1

这是您的示例的重构版本：

[Fact, Trait("Category", "Product")]
public async Task Create_Service_With_Null_Financial_ContactPerson_Should_Fail() {
    // Arrange
    var entity = ObjectFactory.Service.CreateService(packageId = 1);

    var productServiceRepositoryMock = new Mock<IProductServiceRepository>();

    var productPackageRepositoryMock = new Mock<IProductPackageRepository>();
    productPackageRepositoryMock
        .Setup(repository => repository.AnyAsync(It.IsAny<Expression<Func<ProductPackageEntity, bool>>>()))
        .ReturnsAsync(false);

    //Make use of the Lazy<T>(Func<T>()) constructor to return the mock instances
    var lazyProductPackageRepository = new Lazy<IProductPackageRepository>(() => productPackageRepositoryMock.Object);
    var lazyProductServiceRepository = new Lazy<IProductServiceRepository>(() => productServiceRepositoryMock.Object);

    var sut = new ProductServiceService(lazyProductServiceRepository, lazyProductPackageRepository);

    // Act
    var result = await sut.AddServiceAsync(service);

    // Assert
    Assert.False(result.Succeeded);
    Assert.Contains(result.ErrorMessages, error => error.Contains(string.Format(NameMessageResource.NotFoundError, NameMessageResource.ProductPackage)));
}

更新

您所述问题的以下Minimal, Complete, and Verifiable example 经测试通过。

[TestClass]
public class MockLazyOfTWithMoqTest {
    [TestMethod]
    public async Task Method_Under_Test_Should_Return_True() {
        // Arrange
        var productServiceRepositoryMock = new Mock<IProductServiceRepository>();

        var productPackageRepositoryMock = new Mock<IProductPackageRepository>();
        productPackageRepositoryMock
            .Setup(repository => repository.AnyAsync())
            .ReturnsAsync(false);

        //Make use of the Lazy<T>(Func<T>()) constructor to return the mock instances
        var lazyProductPackageRepository = new Lazy<IProductPackageRepository>(() => productPackageRepositoryMock.Object);
        var lazyProductServiceRepository = new Lazy<IProductServiceRepository>(() => productServiceRepositoryMock.Object);

        var sut = new ProductServiceService(lazyProductServiceRepository, lazyProductPackageRepository);

        // Act
        var result = await sut.MethodUnderTest();

        // Assert
        Assert.IsTrue(result);
    }

    public interface IProductServiceService { }
    public interface IProductServiceRepository { }
    public interface IProductPackageRepository { Task<bool> AnyAsync();}

    public class ProductServiceService : IProductServiceService {
        private readonly Lazy<IProductServiceRepository> _repository;
        private readonly Lazy<IProductPackageRepository> _productPackageRepository;

        public ProductServiceService(
            Lazy<IProductServiceRepository> repository,
            Lazy<IProductPackageRepository> productPackageRepository) {
            _repository = repository;
            _productPackageRepository = productPackageRepository;
        }

        public async Task<bool> MethodUnderTest() {
            var errors = new List<ValidationResult>();

            if (!await _productPackageRepository.Value.AnyAsync())
                errors.Add(new ValidationResult("error"));

            return errors.Any();
        }
    }
}

Answer 2

Lazy<> 作为参数有点出乎意料，尽管不是非法的（显然）。请记住，包裹在服务周围的Lazy<> 实际上只是延迟执行工厂方法。为什么不直接将工厂传递给构造函数？您仍然可以在实现类中将对工厂的调用包装在 Lazy<> 中，但随后您可以在测试中伪造/模拟您的工厂并将其传递给您的 sut。

或者，您传递Lazy<> 的原因可能是因为您实际上是在处理单身人士。在这种情况下，我仍然会创建一个工厂并依赖IFactory<>。然后，工厂实现可以在其中包含Lazy<>。

通常，我通过在 IoC 容器中为依赖项设置自定义对象范围来解决单例需求（没有延迟加载）。例如，StructureMap 可以很容易地在 Web 应用程序中将某些依赖项设置为单例或按请求范围。

我很少需要断言我已经对被测系统内的某些服务进行了延迟初始化。我可能需要验证我是否在某个范围内只初始化了一次服务，但这仍然可以通过伪造工厂接口轻松测试。

Answer 3

问题是您正在创建一个 Lazy 的 Mock 作为 fakeProductServiceRepository 并且稍后返回那个只需要一个 Mock 的实例。

你应该改变

var fakeProductServiceRepository = new Mock<Lazy<IProductServiceRepository>>();

到

var fakeProductServiceRepository = new Mock<IProductServiceRepository>();