public void ReturnNull_WhenNotFound() { // Arrange int id = 4; var mockedConversationRepository = new Mock <IEFRepository <Conversation> >(); var conversation = new Conversation(); mockedConversationRepository.Setup(x => x.GetById(id)).Returns(conversation); var mockedUnitOfWork = new Mock <IUnitOfWork>(); var mockedConversationFactory = new Mock <IConversationFactory>(); var mockedMessageService = new Mock <IMessageService>(); var conversationService = new ConversationService( mockedConversationRepository.Object, mockedUnitOfWork.Object, mockedConversationFactory.Object, mockedMessageService.Object); // Act var result = conversationService.GetById(10); // Assert Assert.IsNull(result); }