1 files changed, 17 insertions, 0 deletions
diff --git a/Lib/test/test_descr.py b/Lib/test/test_descr.py
index 707c931..791cf71 100644
--- a/Lib/test/test_descr.py
+++ b/Lib/test/test_descr.py
@@ -4923,6 +4923,23 @@ order (MRO) for bases """
                 cls.lst = [2**i for i in range(10000)]
         X.descr
 
+    def test_remove_subclass(self):
+        # bpo-46417: when the last subclass of a type is deleted,
+        # remove_subclass() clears the internal dictionary of subclasses:
+        # set PyTypeObject.tp_subclasses to NULL. remove_subclass() is called
+        # when a type is deallocated.
+        class Parent:
+            pass
+        self.assertEqual(Parent.__subclasses__(), [])
+
+        class Child(Parent):
+            pass
+        self.assertEqual(Parent.__subclasses__(), [Child])
+
+        del Child
+        gc.collect()
+        self.assertEqual(Parent.__subclasses__(), [])
+
 
 class DictProxyTests(unittest.TestCase):
     def setUp(self):