[Testing Request] Automatically test that diagram containing any elements it may contain can be saved

[sdasda7777]

Given this bug (i.e. diagram not being saveable due to some method not being implemented for some element) appears regularly, I think it would be useful to automatically test that diagram containing any elements it may ever contain can be successfully saved and loaded.

I don't remember the exact details, but I believe child classes may be enumerated, so that might be useful. However perhaps some elements may not be applicable for some diagrams, in which case perhaps diagrams could have associated traits for elements and edges, whose classes would be enumerated instead?