TestDoubles

using System;
using NSubstitute;
using Xunit;

namespace tdd_mvvm
{
  public class LoginPresenterTests
  {
    [Fact]
    public void SubscribeToViewsLoginSubmit()
    {
      var view = Substitute.For<IPresenterView>();

      var subject = new LoginPresenter(view, null);

      view.Received().SubmitLogin += subject.OnLoginSubmitted;
    }

    [Fact]
    public void WhenLoginSubmitIsTriggeredGrabUsernameAndPassword()
    {
      var view = Substitute.For<IPresenterView>();
      var subject = new LoginPresenter(view, null);

      view.SubmitLogin += Raise.EventWith(new object(), new EventArgs());

      var assertUsername = view.Received().Username;
      var assertPassword = view.Received().Password;
    }

    [Fact]
    public void ForwardUsernameAndPasswordToTheAuthenticationServie()
    {
      var view = Substitute.For<IPresenterView>();
      var authService = Substitute.For<IAuthenticationService>();
      var subject = new LoginPresenter(view, authService);
     
      view.SubmitLogin += Raise.EventWith(new object(), new EventArgs());

      authService.Received().Authenticate(Arg.Any<string>, Arg.Any<string>);
    }
  }

  public interface IAuthenticationService
  {
    void Authenticate(string username, string password);
  }

  public interface IPresenterView
  {
    event EventHandler SubmitLogin;
    string Username { get; }
    string Password { get; set; }
  }

  public class LoginPresenter
  {
    private readonly IPresenterView _view;

    public LoginPresenter(IPresenterView view, IAuthenticationService authService)
    {
      _view = view;
      _view.SubmitLogin += OnLoginSubmitted;
    }

    public void OnLoginSubmitted(object source, EventArgs args)
    {
      var username = _view.Username;
    }
  }
}