A change like this should fix the test:

diff --git a/lib/matplotlib/tests/test_animation.py b/lib/matplotlib/tests/test_animation.pyindex 6a9f31733f..a2b35f802c 100644--- a/lib/matplotlib/tests/test_animation.py+++ b/lib/matplotlib/tests/test_animation.py@@ -520,7 +520,7 @@ def test_disable_cache_warning(anim):  def test_movie_writer_invalid_path(anim):     if sys.platform == "win32":-        match_str = r"\[WinError 3] .*'\\\\foo\\\\bar\\\\aardvark'"+        match_str = r"\[WinError 3] .*\\\\foo\\\\bar\\\\aardvark'"     else:         match_str = r"\[Errno 2] .*'/foo"     with pytest.raises(FileNotFoundError, match=match_str):

Do we understand what changed in py313? From looking at the failing string it looks like Python now includes the full path with a drive? Strongly suspect it ispython/cpython#119826 making an internalabspath call more correct.

That seems related from the changelog, but it was backported to 3.12.8, which didn't fail that first time.

Interesting. However, given that this is the text of an error message (and I think including the drive letter is better) I don't think it is worth spending too much time to track it down.

Could bepython/cpython#126780 as the input is a drive-relative path on Windows, and this wasn't backported to 3.12.