This command:

./python -c 'import runpy, typing; runpy.run_module("test")' -R 5:5 test_collections

Sometimes gives spurious failures like this:

test_collections leaked [0, 0, 3, -3, 3] memory blocks, sum=3

I think this is because ABC caches of typing.ChainMap, typing.Counter, and typing.DefaultDict are not cleared by refleak.py/dash_R_cleanup (presumably because inspect.isabstract returns False on those)

Adding a manual clean-up of these cashes to cleanup_cashes() fixes the "leak".