Add test coverage for concurrent set.pop() calls

[CaQtiml]

This test aims for a free-threaded Python.

Testcases in Lib/test/test_free_threading/test_set.py do not cover a case where several threads pop from the same set. So, I want to add a test where .pop is called by several threads on the same set.

My test checks whether the original items are returned exactly once (no duplicates) and the popped set ends up empty.

This is my first time contributing to CPython, so I welcome any advice! I will create a PR soon.

Linked PRs

• gh-158093: Add concurrent test for set.pop() method #158107

[picnixz]

Can you, in a wider search, determine if there are more tests to add for set.* in general? we can then extend the issue instead of having it for a single method.

[picnixz]

Note that such tests may also be elsewhere so be careful.

[CaQtiml]

Can you, in a wider search, determine if there are more tests to add for set.* in general? we can then extend the issue instead of having it for a single method.

What I can quickly come up with now is adding some cases for "add()+remove()" or "copy() during mutation" across multiple threads.

This is my first PR and my first time working with free-threaded Python, so I want to start with a single method to make sure I am on the right track.

[picnixz]

We prefer first knowing the scope of the issue before opening PRs. It is important to understand what is lacking first. I am surprised that we have no such tests and some of that could be found in test_builtins or in other test files.