public async Task GetByIdAsyncWhenInvalidIdReturnsDietNotFoundResponse() { // Arrange var mockDietRepository = GetDefaultIDietRepositoryInstance(); var dietId = 1; mockDietRepository.Setup(r => r.FindById(dietId)) .Returns(Task.FromResult <Diet>(null)); var mockUnitOfWork = GetDefaultIUnitOfWorkInstance(); var service = new DietService(mockDietRepository.Object, mockUnitOfWork.Object); // Act DietResponse result = await service.GetByIdAsync(dietId); var message = result.Message; // Assert message.Should().Be("Diet not found"); }