[3.11] pythongh-116307: Proper fix for 'mod' leaking across importlib…

… tests (pythonGH-116680)

(cherry picked from commit a254807)

Co-authored-by: Jason R. Coombs <[email protected]>
pythongh-116307: Create a new import helper 'isolated modules' and use that instead of 'Clean Import' to ensure that tests from importlib_resources don't leave modules in sys.modules.

Lib/test/support/import_helper.py

@@ -248,6 +248,26 @@ def modules_cleanup(oldmodules):
     sys.modules.update(oldmodules)
 
 
+@contextlib.contextmanager
+def isolated_modules():
+    """
+    Save modules on entry and cleanup on exit.
+    """
+    (saved,) = modules_setup()
+    try:
+        yield
+    finally:
+        modules_cleanup(saved)
+
+
+def mock_register_at_fork(func):
+    # bpo-30599: Mock os.register_at_fork() when importing the random module,
+    # since this function doesn't allow to unregister callbacks and would leak
+    # memory.
+    from unittest import mock
+    return mock.patch('os.register_at_fork', create=True)(func)
+
+
 @contextlib.contextmanager
 def ready_to_import(name=None, source=""):
     from test.support import script_helper

Misc/NEWS.d/next/Tests/2024-03-06-11-00-36.gh-issue-116307.Uij0t_.rst

@@ -0,0 +1,2 @@
+Added import helper ``isolated_modules`` as ``CleanImport`` does not remove
+modules imported during the context.