gh-135552: Add tests that check if weakref for tp_subclasses cleared after finalization - #136304

    def test_clearing_weakrefs_in_gc(self):
        # This test checks that:
        # 1. weakrefs for types with callbacks are cleared before the
        # finalizer is called
        # 2. weakrefs for types without callbacks are cleared after the
        # finalizer is called
        # 3. other weakrefs cleared before the finalizer is called
        errors = []
        class Class:
            def __init__(self):
                self._self = self
                self._1 = weakref.ref(Class, lambda x: None)
                self._2 = weakref.ref(Class)
                self._3 = weakref.ref(self)

            def __del__(self):
                if self._1() is not None:
                    errors.append("Type weakref with callback is not None as expected")
                if self._2() is not Class:
                    errors.append("Type weakref is not Class as expected")
                if self._3() is not None:
                    errors.append("Instance weakref is not None as expected")
        Class()
        gc.collect()
        self.assertEqual(errors, [])