1 files changed, 10 insertions, 0 deletions
diff --git a/Lib/test/test_abc.py b/Lib/test/test_abc.py
index 884dd32..80b0123 100644
--- a/Lib/test/test_abc.py
+++ b/Lib/test/test_abc.py
@@ -81,6 +81,16 @@ class TestABC(unittest.TestCase):
         self.assertEqual(issubclass(C, A), True)
         self.assertEqual(isinstance(c, A), True)
 
+    def test_isinstance_invalidation(self):
+        class A(metaclass=abc.ABCMeta):
+            pass
+        class B:
+            pass
+        b = B()
+        self.assertEqual(isinstance(b, A), False)
+        A.register(B)
+        self.assertEqual(isinstance(b, A), True)
+
     def test_registration_builtins(self):
         class A(metaclass=abc.ABCMeta):
             pass