[3.12] gh-120590: Fix test_pydoc in the refleak hunting mode (GH-120615) (GH-120670)

Mocking only works if sys.modules['pydoc'] and pydoc are the same,
but some pydoc functions reload the module and change sys.modules.
Ensure that sys.modules['pydoc'] is always restored after the corresponding
tests.
(cherry picked from commit 2cf4738)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>

Author: miss-islington

Lib/test/test_pydoc/test_pydoc.py

@@ -378,6 +378,11 @@ def html2text(html):
 
 
 class PydocBaseTest(unittest.TestCase):
+    def tearDown(self):
+        # Self-testing. Mocking only works if sys.modules['pydoc'] and pydoc
+        # are the same. But some pydoc functions reload the module and change
+        # sys.modules, so check that it was restored.
+        self.assertIs(sys.modules['pydoc'], pydoc)
 
     def _restricted_walk_packages(self, walk_packages, path=None):
         """
@@ -409,6 +414,8 @@ def call_url_handler(self, url, expected_title):
 
 class PydocDocTest(unittest.TestCase):
     maxDiff = None
+    def tearDown(self):
+        self.assertIs(sys.modules['pydoc'], pydoc)
 
     @unittest.skipIf(hasattr(sys, 'gettrace') and sys.gettrace(),
                      'trace function introduces __locals__ unexpectedly')
@@ -1151,15 +1158,20 @@ def test_modules_search_builtin(self):
         self.assertTrue(result.startswith(expected))
 
     def test_importfile(self):
-        loaded_pydoc = pydoc.importfile(pydoc.__file__)
+        try:
+            loaded_pydoc = pydoc.importfile(pydoc.__file__)
 
-        self.assertIsNot(loaded_pydoc, pydoc)
-        self.assertEqual(loaded_pydoc.__name__, 'pydoc')
-        self.assertEqual(loaded_pydoc.__file__, pydoc.__file__)
-        self.assertEqual(loaded_pydoc.__spec__, pydoc.__spec__)
+            self.assertIsNot(loaded_pydoc, pydoc)
+            self.assertEqual(loaded_pydoc.__name__, 'pydoc')
+            self.assertEqual(loaded_pydoc.__file__, pydoc.__file__)
+            self.assertEqual(loaded_pydoc.__spec__, pydoc.__spec__)
+        finally:
+            sys.modules['pydoc'] = pydoc
 
 
 class TestDescriptions(unittest.TestCase):
+    def tearDown(self):
+        self.assertIs(sys.modules['pydoc'], pydoc)
 
     def test_module(self):
         # Check that pydocfodder module can be described
@@ -1505,6 +1517,8 @@ def a_fn_with_https_link():
 
 
 class PydocFodderTest(unittest.TestCase):
+    def tearDown(self):
+        self.assertIs(sys.modules['pydoc'], pydoc)
 
     def getsection(self, text, beginline, endline):
         lines = text.splitlines()
@@ -1632,6 +1646,8 @@ def test_html_doc_routines_in_module(self):
 )
 class PydocServerTest(unittest.TestCase):
     """Tests for pydoc._start_server"""
+    def tearDown(self):
+        self.assertIs(sys.modules['pydoc'], pydoc)
 
     def test_server(self):
         # Minimal test that starts the server, checks that it works, then stops
@@ -1694,9 +1710,14 @@ def test_url_requests(self):
             ("foobar", "Pydoc: Error - foobar"),
             ]
 
-        with self.restrict_walk_packages():
-            for url, title in requests:
-                self.call_url_handler(url, title)
+        self.assertIs(sys.modules['pydoc'], pydoc)
+        try:
+            with self.restrict_walk_packages():
+                for url, title in requests:
+                    self.call_url_handler(url, title)
+        finally:
+            # Some requests reload the module and change sys.modules.
+            sys.modules['pydoc'] = pydoc
 
 
 class TestHelper(unittest.TestCase):
@@ -1706,6 +1727,9 @@ def test_keywords(self):
 
 
 class PydocWithMetaClasses(unittest.TestCase):
+    def tearDown(self):
+        self.assertIs(sys.modules['pydoc'], pydoc)
+
     @unittest.skipIf(hasattr(sys, 'gettrace') and sys.gettrace(),
                      'trace function introduces __locals__ unexpectedly')
     @requires_docstrings