deliteful/Toaster widget

OK, I see... I understand from your description how Toaster is supposed to behave w.r.t. keeping/removing holes.   Do you have a test that the end result is that it behaves like the screenshot above?

I'm surprised that you have a test for a private method (i.e. _nonRemovableAreOnlyPersistants()).   I guess it makes sense according to the typical (i.e. non-intern) definition of "unit test", but it's not something we usually do.   Not that it's necessarily a bad thing.   But anyway it would be good to have a test for what the end user sees too.