public void Only_registered_users_can_login()
        {
            var result = _userRegistrationService.ValidateUserAsync("*****@*****.**", "password").Result;

            result.ShouldEqual(UserLoginResults.Successful);

            result = _userRegistrationService.ValidateUserAsync("*****@*****.**", "password").Result;
            result.ShouldEqual(UserLoginResults.NotRegistered);
        }