add module dealloc test

Author: xuantengh

Lib/test/test_weakref.py

@@ -9,6 +9,7 @@
 import copy
 import threading
 import time
+import types
 import random
 import textwrap
 
@@ -2252,6 +2253,13 @@ def test_names(self):
             self.assertEqual(obj.__name__, name)
             self.assertEqual(obj.__qualname__, name)
 
+    def test_module_dealloc(self):
+        mod = types.ModuleType("temp_mod")
+        r = weakref.ref(mod)
+        self.assertIsNotNone(r, "weak ref to a module should not be None")
+
+        del mod
+
 
 libreftest = """ Doctest for examples in the library reference: weakref.rst