public void TestAddUserShouldNotAddExistingUserToTheList() { User newUser = new User { Email = "*****@*****.**", Name = "El Señor", LastName = "De Los Completos", UserName = "******", Password = "******", Administrator = false }; IEnumerable <User> fakeUsers = GetFakeUsers(); Mock <IUserRepository> mockUserRepository = new Mock <IUserRepository>(); IUserManagementService userLogic = new UserManagementService() { UserRepository = mockUserRepository.Object }; mockUserRepository .Setup(wl => wl.Exists(newUser.Email)) .Returns(true); User result = userLogic.Add(newUser); mockUserRepository.VerifyAll(); }