How can I test that "TestProperty" was set a value when ForgotMyPassword(...) was called?

>    public interface IUserRepository    
    {  
        User GetUserById(int n);

    }
    public interface INotificationSender
    {
        void Send(string name);
        int TestProperty { get; set; }
    }

    public class User
    {
        public int Id { get; set; }
        public string Name { get; set; }
    }

    public class LoginController
    {
        private readonly IUserRepository repository;
        private readonly INotificationSender sender;

        public LoginController(IUserRepository repository, INotificationSender sender)
        {
            this.repository = repository;
            this.sender = sender;
        }



        public void ForgotMyPassword(int userId)
        {
            User user = repository.GetUserById(userId);
            sender.Send("Changed password for " + user.Name);
            sender.TestProperty = 1;
        }
    }

    // Sample test to verify that send was called
    [Test]
    public void WhenUserForgetPasswordWillSendNotification_WithConstraints()
    {
        var userRepository = MockRepository.GenerateStub<IUserRepository>();
        var notificationSender = MockRepository.GenerateStub<INotificationSender>();

        userRepository.Stub(x => x.GetUserById(5)).Return(new User { Id = 5, Name = "ayende" });

        new LoginController(userRepository, notificationSender).ForgotMyPassword(5);

        notificationSender.AssertWasCalled(x => x.Send(null),
            options => options.Constraints(Rhino.Mocks.Constraints.Text.StartsWith("Changed")));

      }