`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

refleak テストフレームワークと、atexit コールバックを登録する test_refleak の例から始めます。test_zipimport がモジュールキャッシュをクリアすることで、rlcompleter のモジュールレベルの登録が繰り返し実行される仕組みを調査し、既存の作業についてリンク先の PR gh-139305 と gh-139357 を確認します。完了条件は、有効な atexit 登録が refleak として表示されなくなることです。