This comment is just to note that this change broke our (exotic?) usage of unittest.TestLoader().loadTestsFromName(name) inside a try/except since under Python 3.5 some expected exceptions are no longer raised.

My nasty workaround hack:
https://github.com/biopython/biopython/commit/929fbfbcf2d1ba65ec460a413128dd5e6f68f5bf

I think it is unfortunate that the .errors attribute is just a list of messages as strings, rather than the original exception object(s) which would be easier to handle (e.g. using the subclass hierarchy).