public void User_exists()
        {
            var fluentApi = UserApiThatReturnsUser("*****@*****.**");

            var userSignupApi = MockRepository.GenerateStub <IFluentApi <UserSignup> >();
            var userApi       = new UserApi(fluentApi, userSignupApi);

            var checkUserExists = userApi.CheckUserExists("*****@*****.**");

            Assert.That(checkUserExists);
        }