XUnit模拟方法，但不返回预期结果

Question

I am using moq in XUnit test but for some reason the mock is not working properly. Here's my unit test:

 [Fact]
        public async Task SampleUnitTest()
        {
            //Arrange
            var httpClient = new HttpClient(new FakeHttpMessageHandler());
            _mockConstructRequest.Setup(x => x.ConstructRequestString(searchRequestModel))
                                 .Returns("a sample string");
            var service = new LibraryService(_mockConstructRequest.Object);

            //Act
            var response = service.GetResponse(new Request(), httpClient);

            //Assert
            response.Should().BeNull();

        }

         private class FakeHttpMessageHandler : HttpMessageHandler
        {
            public Func<HttpRequestMessage, CancellationToken, HttpResponseMessage> HttpRequestHandler { get; set; } =
            (r, c) =>
                new HttpResponseMessage
                {
                    ReasonPhrase = r.RequestUri.AbsoluteUri,
                    StatusCode = HttpStatusCode.OK
                };


            protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
            {
                return Task.FromResult(HttpRequestHandler(request, cancellationToken));
            }
        } 

And here is the actual code and I am trying to test GetResponse method.

  public class LibraryService : ILibraryService
 {
    private IConfiguration _configuration;
    private IRequestConstructor _requestContructor;
    public LibraryService (IRequestConstructor requestConstructor)
    {
        _requestConstructor = requestConstructor;
    }

    public async Task<Response> GetResponse(Request request, HttpClient client)
        {

            //construct request
            string requestString = _constructRequestString.ConstructRequestString(request, client);

            return null;
        }
 }

 public class RequestContructor : IRequestContructor
 {
  public string ConstructRequestString(Request request)
        {
            return "a request string";
        }
 }

I was trying to step through the code from my unit test but when the break point is at this line, requestString variable is null while it is supposed to return "a sample string". Anyone knows why?

string requestString = _constructRequestString.ConstructRequestString(request, client);

Answer 1

As far as I can see you are mocking incorrectly: Your mock:

_mockConstructRequest.Setup(x => x.ConstructRequestString(searchRequestModel))
                                 .Returns("a sample string");

Method you are calling:

_constructRequestString.ConstructRequestString(request, client);

Should not it be something like this:

_mockConstructRequest.Setup(x => x.ConstructRequestString(It.IsAny<Request>(),It.IsAny<HttpClient>()))
                                 .Returns("a sample string");

On top of that:

Try to initialize your mocks and your "classUnderTest" in constructor instead of in each test, it will run each time before the test and will do everything for you. For example:

public class UnitTestClass{

private readonly ClassUnderTest _classUnderTest;
private readonly Mock<ClassUnderTestDependecy> mockedInstance;

public UnitTestClass {
mockedInstance= new Mock<ClassUnderTestDependecy>();
_classUnderTest= new ClassUnderTest (ClassUnderTestDependecy.Object);
}

}