Added more tests for issue #27122.

1 files changed, 34 insertions, 1 deletions

diff --git a/Lib/test/test_contextlib.py b/Lib/test/test_contextlib.py
index 516403ef65..c04c804af5 100644
--- a/Lib/test/test_contextlib.py
+++ b/Lib/test/test_contextlib.py
@@ -12,6 +12,39 @@ except ImportError:
     threading = None
 
 
+class TestAbstractContextManager(unittest.TestCase):
+
+    def test_enter(self):
+        class DefaultEnter(AbstractContextManager):
+            def __exit__(self, *args):
+                super().__exit__(*args)
+
+        manager = DefaultEnter()
+        self.assertIs(manager.__enter__(), manager)
+
+    def test_exit_is_abstract(self):
+        class MissingExit(AbstractContextManager):
+            pass
+
+        with self.assertRaises(TypeError):
+            MissingExit()
+
+    def test_structural_subclassing(self):
+        class ManagerFromScratch:
+            def __enter__(self):
+                return self
+            def __exit__(self, exc_type, exc_value, traceback):
+                return None
+
+        self.assertTrue(issubclass(ManagerFromScratch, AbstractContextManager))
+
+        class DefaultEnter(AbstractContextManager):
+            def __exit__(self, *args):
+                super().__exit__(*args)
+
+        self.assertTrue(issubclass(DefaultEnter, AbstractContextManager))
+
+
 class ContextManagerTestCase(unittest.TestCase):
 
     def test_contextmanager_plain(self):
@@ -89,7 +122,7 @@ class ContextManagerTestCase(unittest.TestCase):
         def woohoo():
             yield
         try:
-            with self.assertWarnsRegex(PendingDeprecationWarning,
+            with self.assertWarnsRegex(DeprecationWarning,
                                        "StopIteration"):
                 with woohoo():
                     raise stop_exc