Add tests for the generic descriptors

Author: encukou

Lib/test/test_descr.py

@@ -6013,5 +6013,69 @@ class A(metaclass=M):
                 pass
 
 
+class TestGenericDescriptors(unittest.TestCase):
+    def test___dict__(self):
+        class CustomClass:
+            pass
+        class SlotClass:
+            __slots__ = ['foo']
+        class SlotSubClass(SlotClass):
+            pass
+        class IntSubclass(int):
+            pass
+
+        dict_descriptor = CustomClass.__dict__['__dict__']
+        self.assertEqual(dict_descriptor.__objclass__, object)
+
+        for cls in CustomClass, SlotSubClass, IntSubclass:
+            with self.subTest(cls=cls):
+                self.assertIs(cls.__dict__['__dict__'], dict_descriptor)
+                instance = cls()
+                instance.attr = 123
+                self.assertEqual(
+                    dict_descriptor.__get__(instance, cls),
+                    {'attr': 123},
+                )
+        with self.assertRaises(AttributeError):
+            print(dict_descriptor.__get__(True, bool))
+        with self.assertRaises(AttributeError):
+            print(dict_descriptor.__get__(SlotClass(), SlotClass))
+
+        # delegation to type.__dict__
+        self.assertIsInstance(
+            dict_descriptor.__get__(type, type),
+            types.MappingProxyType,
+        )
+
+    def test___weakref__(self):
+        class CustomClass:
+            pass
+        class SlotClass:
+            __slots__ = ['foo']
+        class SlotSubClass(SlotClass):
+            pass
+        class IntSubclass(int):
+            pass
+
+        weakref_descriptor = CustomClass.__dict__['__weakref__']
+        self.assertEqual(weakref_descriptor.__objclass__, object)
+
+        for cls in CustomClass, SlotSubClass:
+            with self.subTest(cls=cls):
+                self.assertIs(cls.__dict__['__weakref__'], weakref_descriptor)
+                instance = cls()
+                instance.attr = 123
+                self.assertEqual(
+                    weakref_descriptor.__get__(instance, cls),
+                    None,
+                )
+        with self.assertRaises(AttributeError):
+            print(weakref_descriptor.__get__(True, bool))
+        with self.assertRaises(AttributeError):
+            print(weakref_descriptor.__get__(SlotClass(), SlotClass))
+        with self.assertRaises(AttributeError):
+            print(weakref_descriptor.__get__(IntSubclass(), IntSubclass))
+
+
 if __name__ == "__main__":
     unittest.main()