[flexcoders] Is there a way to mock stage?

[Borek]

My scenario: a user can click on a "full screen" button which calls Presenter's 
setFullScreen() method. I'd like to unit test this method but am not sure how.

If the unit test wasn't required, I would probably do something like this in my 
Presenter:

public function setFullScreen() : void {
  view.stage.displayState = StageDisplayState.FULL_SCREEN;
  // 'view' is a reference to the screen which Presenter looks after
}

However, this is hard to test. If I try this:

[Test]
public function can_set_normal_screen_mode() : void {
  var settingsPresenter : SettingsPresenter = new SettingsPresenter(new 
SettingsViewStub());
  settingsPresenter.setFullScreen;

  var view : UIComponent = UIComponent(settingsPresenter.view);
  assertTrue(view.stage.displayState == StageDisplayState.FULL_SCREEN);
}

I get null reference error because the view hasn't been added to a display list 
yet and therefore stage is null. I don't really want to add the stub view to 
the display list because that's not the point of testing a Presenter, is it?

So I thought I would mock view.stage to contain my implementation of Stage but 
calling new Stage() or new MySubclassOfStage() fails because Stage can't be 
instantiated using the new keyword.

Right now, I am thinking about moving the actual call to stage.displayState = 
... to the View itself and just call this method from the presenter. I won't be 
able to test if stage's property has been set correctly (or at least not 
easily) but I can see no better way at the moment.

Any suggestions?

Thanks,
Borek