public async void GetResultsByUserAsync_GivenInvalidUser_ShouldProduceErrorMessage() { // arrange var mockUnitOfWork = new Mock <IUnitOfWork>(); var mockDTOMapper = new Mock <IDTOMapper>(); var evaluationService = new EvaluationService(mockUnitOfWork.Object, mockDTOMapper.Object); string expected = "username should be alphanumeric"; // act var actual = await evaluationService.GetResultsByUserAsync("@"); // assert Assert.Equal(expected, actual.ErrorMessage); }