regrtest --parallel-threads shares TestCase._cleanups between threads #160543

Bug report

regrtest's --parallel-threads runs the same test concurrently in multiple threads. To do so it creates independent copies of the tests using copy.copy():

copy.copy() does a shallow copy, so the test's _cleanups list is shared between threads. Each thread runs the test's doCleanup method, popping and running methods from _cleanups until it's empty:

Some cleanup functions may run more than once in a thread or may not run at all, because _cleanups is shared across all threads.

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Linked PRs

• gh-160543: Isolate cleanup stacks in parallel test workers #160560