`atexit` module breaks refleak check

Bug report

Bug description:

If the test registers a callback with atexit module, refleak test will consider it a leak.

    def test_refleak(self):
        atexit.register(lambda: None)

This is the root cause of the buildbot failure of https://github.com/python/cpython/pull/139185. It's a couple of coincidences that caused the seemingly unrelated issue. Basically, clearing the module cache in test_zipimport made the module-level code in rlcompleter, which includes a register to atexit, run more than once.

There are a few possible approaches to fix this, but I did not find the solution that I'm immediately happy with.

I consider this a test framework bug as this should be a valid behavior. The ideal solution is to keep the atexit callbacks before running test in a loop and restore it after. However, atexit does not provide such an interface, public or private. You can either clear it or run it. The callbacks are stored in a state of the interpreter and we don't have any access to it.

Without that, we either need to somehow calculate the allocated memory by atexit, or hope that no one writes a test that writes to atexit. Of course there might be other ways that I did not think of.

CPython versions tested on:

CPython main branch

Operating systems tested on:

macOS

Linked PRs

• gh-139305
• gh-139357

• [3.14] gh-139305 was backported as part of gh-139280

Inizia con il framework di test refleak e con l'esempio test_refleak che registra un callback atexit. Esamina come la cancellazione della cache dei moduli da parte di test_zipimport faccia eseguire ripetutamente la registrazione a livello di modulo di rlcompleter, e consulta le PR collegate gh-139305 e gh-139357 per verificare il lavoro già esistente. Il lavoro è completo quando le registrazioni atexit valide non vengono più visualizzate come refleaks.