Result from mocking unit test always returns null

Question

I'm currently setting up some unit tests to return ID of the cafes using some mocking, but for some reason the result variable always returns null.

Setup in service class which implements the Get method

public async Task<CafeResponse> Get(int cafeId)
        {
            var cafe= await _cafeRepository.GetByIdAsync(cafeId);

            
            return _mapper.Map<CafeResponse>(cafe);
        }

Unit test setup: Currently the result variable shows null? Not sure if this is due to me setting up the mock incorrectly

        [Fact]
        public async Task Get_ShouldReturnCafeArray_WhenCafesInDatabase()
        {
            //Arrange
            var cafeId = 98;
            var cafeName = "bellas";
            var cafeIdGuid = Guid.NewGuid();
            var cafeDesc = "this is my test";
            var cafeTypeId = 1;


            var cafeDto = new Cafe
            {
                CafeId = cafeId,
                Name = cafeName,
                CafeGuid = cafeIdGuid, 
                Description = cafeDesc,
                CafeTypeId = cafeTypeId,
            
            };

            var expected = new CafeResponse();

            var mockCafe = new Mock<IRepositoryAsync<Cafe>>();
            mockCafe.Setup(x => x.GetByIdAsync(cafeId)).ReturnsAsync(cafeDto);

           
            var mockMapper = new Mock<IMapper>();
            mockMapper.Setup(x => x.Map<Cafe, CafeResponse>(It.IsAny<Cafe>())).Returns(expected);

            //Act
            var cafeService = new CafeService(mockCafe.Object, mockMapper.Object);
            var result = await cafeService.Get(cafeId); //always returns null

           
            //Assert
            mockCafe.Verify(x => x.GetByIdAsync(cafeId), Times.Once);
            Assert.Equal(cafeId, result.CafeId);


        }

Are you expecting a filled out cafe response from your mapper? Currently, your mockMapper is returning a blank CafeResponse. — Ben Sampica
yep i am expecting a cafe response from the mapper, wanted to add more asserts for further testing — James McCoy
@BenSampica I thought I implemented it correctly? Why is it returning a blank response? — James McCoy
because of this line mockMapper.Setup(x => x.Map<Cafe, CafeResponse>(It.IsAny<Cafe>())).Returns(expected);.expected variable is an empty object — ilkerkaran
I've got a mapper setup in my service class as well maybe I should be trying to use that instead of creating one in this class? — James McCoy

devNull devNull · Accepted Answer · 2020-07-26T23:48:20

The reason that you're getting a null result with the code that you have is because for IMapper you're mocking:

TDestination Map<TSource, TDestination>(TSource source);

but your actual code is using:

TDestination Map<TDestination>(object source);

So if you just want the test to return your "expected" instance of CafeResponse, then you need to update your Mock<IMapper> setup to be:

mockMapper.Setup(x => x.Map<CafeResponse>(It.IsAny<Cafe>())).Returns(expected);

The more appropriate solution as pointed out in the comments would be to simply create a Mapper instance for your test:

var mapper = new MapperConfiguration(cfg =>
{
    cfg.AddProfile<MyProfile>();
}).CreateMapper();

Otherwise, you're just testing that you're mock is returning what you tell it to and not really verifying any functionality in your code.

Result from mocking unit test always returns null

1 Answers