bpo-33747: Avoid mutating the global sys.modules dict in unittest.mock tests (GH-8520)

Lib/unittest/test/testmock/testpatch.py

@@ -9,6 +9,7 @@ import unittest
 from unittest.test.testmock import support
 from unittest.test.testmock.support import SomeClass, is_instance
 
+from test.test_importlib.util import uncache
 from unittest.mock import (
     NonCallableMock, CallableMixin, sentinel,
     MagicMock, Mock, NonCallableMagicMock, patch, _patch,
@@ -1660,21 +1661,20 @@ class PatchTest(unittest.TestCase):
 
 
     def test_patch_imports_lazily(self):
-        sys.modules.pop('squizz', None)
-
         p1 = patch('squizz.squozz')
         self.assertRaises(ImportError, p1.start)
 
+        with uncache('squizz'):
             squizz = Mock()
-        squizz.squozz = 6
             sys.modules['squizz'] = squizz
+
+            squizz.squozz = 6
             p1 = patch('squizz.squozz')
             squizz.squozz = 3
             p1.start()
             p1.stop()
         self.assertEqual(squizz.squozz, 3)
 
-
     def test_patch_propogrates_exc_on_exit(self):
         class holder:
             exc_info = None, None, None
@@ -1696,7 +1696,12 @@ class PatchTest(unittest.TestCase):
         def test(mock):
             raise RuntimeError
 
+        with uncache('squizz'):
+            squizz = Mock()
+            sys.modules['squizz'] = squizz
+
             self.assertRaises(RuntimeError, test)
+
         self.assertIs(holder.exc_info[0], RuntimeError)
         self.assertIsNotNone(holder.exc_info[1],
                             'exception value not propgated')