gh-110525: Add tests for internal set CAPI

[sobolevn]

• Issue: Improve CAPI tests of set and frozenset #110525

[serhiy-storchaka]

What if it returns 2 or -2?

Suggested change

	if (rc == 1) {
	if (rc != 0 && rc != -1) {

[sobolevn]

Sorry, I don't understand this one. Right now it is defined as:

cpython/Objects/setobject.c

Lines 2332 to 2346 in 66a9b10

	int
	_PySet_NextEntry(PyObject *set, Py_ssize_t *pos, PyObject **key, Py_hash_t *hash)
	{
	setentry *entry;
	if (!PyAnySet_Check(set)) {
	PyErr_BadInternalCall();
	return -1;
	}
	if (set_next((PySetObject *)set, pos, &entry) == 0)
	return 0;
	*key = entry->key;
	*hash = entry->hash;
	return 1;
	}

It cannot return anything except [-1, 0, 1].
Do you mean that it can return something other than [-1, 0, 1] in the future?
I think that our test case must catch this change and be adapted if needed.

This function is not documented currently.

[serhiy-storchaka]

The purpose of the test is to verify our assumptions (that it cannot return anything except [-1, 0, 1]). Otherwise there would not be need of tests.

In future a new return can be added in the code, or refactoring can lead to returning non-initialized variable in rare case. The wrapper will successfully return None.

[sobolevn]

Got it, I used an assertion, which is more readable in my opinion 👍

[miss-islington]

Thanks @sobolevn for the PR, and @serhiy-storchaka for merging it 🌮🎉.. I'm working now to backport this PR to: 3.12.
🐍🍒⛏🤖

[miss-islington]

Sorry, @sobolevn and @serhiy-storchaka, I could not cleanly backport this to 3.12 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker 9cfb4e0d1ebf2900c19ee07697818c621f46cc3d 3.12

[sobolevn]

Working on a backport

[sobolevn]

@serhiy-storchaka looks like #108787 never got backported, so we don't have the same file structure on 3.12