Javafx : Dialog pane reference

I have a controller, which contains buttons, if I press one button an Alert shows, with Yes and No options, and I want to write a test for this controller class testing the result of this Alert, for example if I press the Yes button what happens. I could get the Window/Stage, and the Scene, but how can I get the Alert from the controller which popped up. Is that the primaryStage or I don't really understand how can I get it. I had a look at the hierarchy of the Alert and it doesn't have any relation with the Stage or Scene or just I didn't observed it. Is there a possibility to get a reference of the Alert or of its buttons?