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, [])