gh-150175: Fix ThreadingMock call_count race condition (GH-150176)

ThreadingMock._increment_mock_call() was not thread-safe.
Multiple threads calling the mock simultaneously could lose
increments due to race conditions on call_count and other
attributes.

Fix by overriding _increment_mock_call in ThreadingMixin
and wrapping it with the existing _mock_calls_events_lock.
(cherry picked from commit 388e023)

Co-authored-by: saisneha196 <156835592+saisneha196@users.noreply.github.com>

Author: saisneha196

Lib/unittest/mock.py

@@ -3121,6 +3121,10 @@ def _mock_call(self, *args, **kwargs):
 
         return ret_value
 
+    def _increment_mock_call(self, /, *args, **kwargs):
+        with self._mock_calls_events_lock:
+            super()._increment_mock_call(*args, **kwargs)
+
     def wait_until_called(self, *, timeout=_timeout_unset):
         """Wait until the mock object is called.
 

Misc/NEWS.d/next/Library/2026-05-21-11-25-58.gh-issue-150175.8H4Caz.rst

@@ -0,0 +1,3 @@
+Fix race condition in :class:`unittest.mock.ThreadingMock` where
+concurrent calls could lose increments to ``call_count`` and other
+attributes due to a missing lock in ``_increment_mock_call``.