I'd suggest that the right fix here would be to move warnoptions into the config struct as proposed in the PEP: https://www.python.org/dev/peps/pep-0432/#supported-configuration-settings

The main reason we merged this as a private API was so we could do that setting-by-setting, with the test suite ensuring we weren't breaking anything.

It looks like in this case, it's the status quo that's broken, and the change makes it possible to fix it :)