I have a vague notion of asserting that "all classes implement their interfaces".
It would remove a good amount of boilerplate tests as well as assuring me that nobody forgot to write their interface assertions.

The part I don't have figured out is how to make sure all classes are loaded up into python at the time of assertion.
I could make a bit of code that walks the file system looking for python modules and attempts to import "everything" before the assertion runs, but that kind of code is always messy and filled with flawed edge cases, at least when I write it.