At the very last resort you'd get the Homescreen!
I just feel `switch_to_displayed_app` is ambiguous and by using it we're accepting that ambiguity and prepared for the app to be the wrong one eg last window/frame not closed properly.
calling it from an app object directly like `self.phone.switch_to_displayed_app()` suggests to me that you should be getting that app's frame most of the time.
It juts feels more like a global action rather than one applicable to the app under test :)