不能在单元测试中使用模拟接口 class

Question

I'm trying to mock a method in my Unit Test but I can't debug into the the method from the service.

I have a service with the method DoSomething1 that I want to test:

public MyService : IMyService
{
    private IAnotherService _anotherService;

    public MyService(IAnotherService anotherService)
    {
        _anotherService = anotherService;
    }

    public async Task DoSomething1(string param)
    {
        // Code...
        _anotherService.DoSomething2(string param1, string param2);
        // Code...
    }
}

This is my testing class:

[TestClass]
public class MyServiceTests : TestBase
{
    private Mock<IAnotherService> _mockAnotherService;
    
    [TestInitialize]
    public void Setup()
    {
        _mockAnotherService = new Mock<IAnotherService>();
    }

    [TestMethod]
    public async Task Test_MyService_DoSomething()
    {
        var myService = new MyService(_mockAnotherService.Object);

        var result = myService.DoSomething1(param1);

        // Some Asserts...
    }
}

If I now debug it I can get into MyService but I can't debug into

_anotherService.DoSomething2(string param1, string param2);

And it will fail my tests.

Using this works but seems to be bad practice:

var myService = Container.GetInstance<MyService>();

What am I missing?

Answer 1

The purpose of a mock is to be a stand-in for the real thing. In testing scenarios it is often undesirable to have the whole object graph wired up, because it is often hard to set up, parts of it might interact with resources that are not available/slow/unreliable, or it might make it much harder, if not impossible to invoke certain edge cases or error scenarios.

In a comment you state that using Container.GetInstance<MyService>() instead of setting it up with a mock is passing your tests. This means you are using the real implementation of IAnotherService . If this is not posing any problems then do that. If you are unable to invoke certain test cases with "the real thing" or it turns out that your tests become brittle or slow, then mock it.

If you use a mock of IAnotherService then the instance of it is not going to do anything by itself. You can tell the mock to return something, but that is pretty much it. eg

_mockAnotherService.Setup(m => m.DoSomething2("a", "b")).Returns(42);

The mock wont be able to simulate any side effects (ie writing to a DB or file). You have to simulate that directly in your test. Debugging into the mocked version of DoSomething2() , if it were possible for you, would only show you how the Moq is implementing its mocks. Assume that they are doing the right thing and that it makes no sense to debug. It is not the real DoSomething2() .