单元测试和Moq'ing构造函数参数问题

Question

Question Background:

I'm currently trying to unit test an MVC4 WebApi project.

The structure of this project uses a facade class injected into the constructor of the relevant controller. This is all achieved with Unity to keep close coupling to an absolute minimum.

Even thought Unity is being implemented, in the Unit tests I'm setting the product controllers up as follows:

var repositoryFacade = new RepositoryFacade(new RepositorySelector(new RepositoryGenerator()));

var productController = new ProductController(repositoryFacade)

The following piece of code shows the 'GetProducts' method of the controller class:

public ProductController(IRepositoryFacade facade)
    {
        _facade = facade;

        productRepository = _facade.GetProductRepository();
    }

    public List<Product> GetProducts()
    {
        return productRepository.GetProducts();
    }

Where the code is currently at:

If I simply want to test how many times this method is hit, I tried setting my UnitTest up as follows, using the Moq framework:

[TestMethod]
    public void Test_The_GetAllProducts_Method_is_Called()
    {

        var mockRepositoryGenerator = new Mock<IRepositoryGenerator>();

        var mockRepositorySelector = new Mock<IRepositorySelector>(mockRepositoryGenerator.Object);

        var mockFacade = new Mock<IRepositoryFacade>(mockRepositorySelector.Object);

        mockFacade.Setup(x => x.GetProductRepositoryV1().GetProducts());

        var productController = new ProductV1Controller(mockFacade.Object);

        var returnedProducts = productController.GetProducts();

        mockFacade.VerifyAll();
    }

The problem:

Currently I'm getting errors when trying to set the constructor of the mocked objects in the test, as shown:

Constructor arguments cannot be passed for interface mocks.

I understand this as I'm Moq'ing the interface and there is no constructor, but this is also where my learning knowledge of Unit Tests and mocking is a bit bare.

Can anyone tell me how I would correctly go about mocking this test out?

Answer 1

Your controller depends on repository. It's better to make this dependency explicit:

public ProductController(IProductRepository productRepository)
{
    _productRepository = productRepository;
}

public List<Product> GetProducts()
{
    return _productRepository.GetProducts();
}

Testing becomes much easier also:

ProductV1Controller _productController;
Mock<IProductRepository> _mockRepository;

[TestInitialize]
public void TestInitialize()
{
    _mockRepository = new Mock<IProductRepository>();
    _productController = new ProductV1Controller(_mockRepository.Object);
}

[TestMethod]
public void ShouldLoadAllProducts()
{       
    _mockRepository.Setup(r => r.GetProducts()).Return(SomeProducts);

    var returnedProducts = _productController.GetProducts();

    Assert.Equals(returnedProducts, SomeProducts);
    _mockRepository.VerifyAll();
}

Answer 2

Your problem is here (and other lines like it):

var mockRepositoryGenerator = new Mock<IRepositoryGenerator>();

var mockRepositorySelector = new Mock<IRepositorySelector>(mockRepositoryGenerator.Object);

As you say, you are attempting to create a Mock of IRepositorySelector, and passing the previously mocked IRepositoryGenerator in as a constructor argument. But Interfaces have no inherent constructors, so it doesn't know what to do with it.

You should expose a property on the interface that takes the IRepositoryGenerator (if you haven't got one already), then set it after you have mocked the interface:

var mockRepositoryGenerator = new Mock<IRepositoryGenerator>();

var mockRepositorySelector = new Mock<IRepositorySelector>();
mockRepositorySelector.Generator = mockRepositoryGenerator.Object;