public void InvalidUserCreationTet()
        {

            var dataAccess = Mock.Interface<IDataAccess>();
            var userService = new UserService(dataAccess);

            Assert.Throws<ValidationException>(() =>
            {
                var newUser = new User();
                userService.CreateUser(newUser);
            });

        }
        public void CreateNullUserTest()
        {

            var dataAccess = Mock.Interface<IDataAccess>();
            var userService = new UserService(dataAccess);

            Assert.Throws<ArgumentNullException>(() =>
            {
                User newUser = null;
                userService.CreateUser(newUser);
            });

        }