I’ve just tried to compile from the 3.1.0rc1 tag for ArchLinux to see if everything runs OK, but I’ve noticed that the large bunch of tests files (usr/lib/python3.7/site-packages/matplotlib/tests/, usr/lib/python3.7/site-packages/matplotlib/sphinxext/tests/ and usr/lib/python3.7/site-packages/mpl_toolkits/tests/) got installed while we don’t have any specific setup.cfg, so that tests should not be installed as is the default (and has been for the past years/releases).

I can provide more information if required, just tell me what (and eventually where to look for them).