Make `test_c_subclass_of_heap_ctype_with_tpdealloc_decrefs_once` and `test_c_subclass_of_heap_ctype_with_del_modifying_dunder_class_only_decrefs_once` behavioral tests

[mpage]

Feature or enhancement

Proposal:

The test_c_subclass_of_heap_ctype_with_tpdealloc_decrefs_once and test_c_subclass_of_heap_ctype_with_del_modifying_dunder_class_only_decrefs_once tests were added to verify that we don't decref a type object too many times when destroying an instance of the type in certain scenarios. The tests currently verify this by checking reference counts. This is sensitive to implementation details and likely to break in the future. To make this more robust, we'd like to refactor the tests and supporting C code to verify that we don't crash (a symptom of decrefing too many times).

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Links to previous discussion of this feature:

No response