Ah, perhaps IPython 7.0.0 is a bit too old for Python 3.9 which was release Oct 5, 2020. Based on release dates, it seems like we should aim forat least IPython 7.19, released Oct 30, 2020? I didn't find any specific release notes about it except for "I’ve started to test on Python 3.9PR #12307 and fix some errors." in 7.15.

I think we need to change the last line oflib/matplotlib/testing/__init__.py from

assertproc.stdout.strip()==f"Out[1]: '{expected_backend}'"

to something like

assertproc.stdout.strip().endswith(f"'{expected_backend}'")

as under some circumstances when I'm running old ipython but newish everything else I get (ignoring newlines)

Out[1]: Installed osx event loop hook. 'MacOSX'

Thanks for doing this, I didn't look very far back when I added these tests.

Locally I've tried this branch on Python 3.9 on a mac (to run both theqt andosx tests) with progressively older ipython, and it works (as in the tests pass) for ipython >= 7.3.0 but fails for ipython < 7.3.0. Ipython 7.3.0 was released in February 2019 so pre-dates Python 3.9 by a good year and a half but still seems to work with it. So officially covering >= 7.19 seems good to me as it is rule-based on the Python 3.9 release date.

Err, that was a bit premature as tests weren't passing yet.

🤦🏻 Sorry, I only saw the coverage failure and missed the real failure.