I'd rather have our own test pyd that shows a minimal repro of the behavior. Requiring pywin32 for running one test is excessive, won't reveal the issue (if it exists) on other platforms, and is not necessarily going to help someone debug the issue.

I agree this is probably due to PEP 489, which means that Eric is almost certainly the best person to look into it. It may also be due to the list of suffixes changing for 3.5 (".cp35-win32.pyd" is now a valid suffix as well as just ".pyd", for example), but looking at pywintypes.py that seems unlikely.