I'm analysing the Magritte system and I can see that there are many classes that haven't been declared. Some, I believe, are those are there only to be abstracted like MABasicObject. Some others, like MAAccessorMock, are there only for testing purpose? And some other ones, like MAPropertyError, have blank code but still have some references to themselves.

So are all they code left blank intentionally for future work or for just testing, or just an incomplete work. Should they be considered bad smells code as I am analysing those.

Thank you very much!