1 files changed, 86 insertions, 0 deletions
diff --git a/Lib/test/test_capi.py b/Lib/test/test_capi.py
index 7b35ba6..4d6e2f2 100644
--- a/Lib/test/test_capi.py
+++ b/Lib/test/test_capi.py
@@ -383,6 +383,92 @@ class CAPITest(unittest.TestCase):
             del L
             self.assertEqual(PyList.num, 0)
 
+    def test_subclass_of_heap_gc_ctype_with_tpdealloc_decrefs_once(self):
+        class HeapGcCTypeSubclass(_testcapi.HeapGcCType):
+            def __init__(self):
+                self.value2 = 20
+                super().__init__()
+
+        subclass_instance = HeapGcCTypeSubclass()
+        type_refcnt = sys.getrefcount(HeapGcCTypeSubclass)
+
+        # Test that subclass instance was fully created
+        self.assertEqual(subclass_instance.value, 10)
+        self.assertEqual(subclass_instance.value2, 20)
+
+        # Test that the type reference count is only decremented once
+        del subclass_instance
+        self.assertEqual(type_refcnt - 1, sys.getrefcount(HeapGcCTypeSubclass))
+
+    def test_subclass_of_heap_gc_ctype_with_del_modifying_dunder_class_only_decrefs_once(self):
+        class A(_testcapi.HeapGcCType):
+            def __init__(self):
+                self.value2 = 20
+                super().__init__()
+
+        class B(A):
+            def __init__(self):
+                super().__init__()
+
+            def __del__(self):
+                self.__class__ = A
+                A.refcnt_in_del = sys.getrefcount(A)
+                B.refcnt_in_del = sys.getrefcount(B)
+
+        subclass_instance = B()
+        type_refcnt = sys.getrefcount(B)
+        new_type_refcnt = sys.getrefcount(A)
+
+        # Test that subclass instance was fully created
+        self.assertEqual(subclass_instance.value, 10)
+        self.assertEqual(subclass_instance.value2, 20)
+
+        del subclass_instance
+
+        # Test that setting __class__ modified the reference counts of the types
+        self.assertEqual(type_refcnt - 1, B.refcnt_in_del)
+        self.assertEqual(new_type_refcnt + 1, A.refcnt_in_del)
+
+        # Test that the original type already has decreased its refcnt
+        self.assertEqual(type_refcnt - 1, sys.getrefcount(B))
+
+        # Test that subtype_dealloc decref the newly assigned __class__ only once
+        self.assertEqual(new_type_refcnt, sys.getrefcount(A))
+
+    def test_c_subclass_of_heap_ctype_with_tpdealloc_decrefs_once(self):
+        subclass_instance = _testcapi.HeapCTypeSubclass()
+        type_refcnt = sys.getrefcount(_testcapi.HeapCTypeSubclass)
+
+        # Test that subclass instance was fully created
+        self.assertEqual(subclass_instance.value, 10)
+        self.assertEqual(subclass_instance.value2, 20)
+
+        # Test that the type reference count is only decremented once
+        del subclass_instance
+        self.assertEqual(type_refcnt - 1, sys.getrefcount(_testcapi.HeapCTypeSubclass))
+
+    def test_c_subclass_of_heap_ctype_with_del_modifying_dunder_class_only_decrefs_once(self):
+        subclass_instance = _testcapi.HeapCTypeSubclassWithFinalizer()
+        type_refcnt = sys.getrefcount(_testcapi.HeapCTypeSubclassWithFinalizer)
+        new_type_refcnt = sys.getrefcount(_testcapi.HeapCTypeSubclass)
+
+        # Test that subclass instance was fully created
+        self.assertEqual(subclass_instance.value, 10)
+        self.assertEqual(subclass_instance.value2, 20)
+
+        # The tp_finalize slot will set __class__ to HeapCTypeSubclass
+        del subclass_instance
+
+        # Test that setting __class__ modified the reference counts of the types
+        self.assertEqual(type_refcnt - 1, _testcapi.HeapCTypeSubclassWithFinalizer.refcnt_in_del)
+        self.assertEqual(new_type_refcnt + 1, _testcapi.HeapCTypeSubclass.refcnt_in_del)
+
+        # Test that the original type already has decreased its refcnt
+        self.assertEqual(type_refcnt - 1, sys.getrefcount(_testcapi.HeapCTypeSubclassWithFinalizer))
+
+        # Test that subtype_dealloc decref the newly assigned __class__ only once
+        self.assertEqual(new_type_refcnt, sys.getrefcount(_testcapi.HeapCTypeSubclass))
+
 
 class TestPendingCalls(unittest.TestCase):