demonstrate that the test fails on main

Author: chaope

Lib/test/test_unittest/testmock/testthreadingmock.py

@@ -1,5 +1,6 @@
 import time
 import unittest
+import threading
 import concurrent.futures
 
 from test.support import threading_helper
@@ -196,6 +197,22 @@ def test_reset_mock_resets_wait(self):
         m.wait_until_any_call_with()
         m.assert_called_once()
 
+    def test_call_count_thread_safe(self):
+        m = ThreadingMock()
+        # 3k loops reliably reproduces the issue while keeping runtime ~0.6s
+        LOOPS = 3_000
+        THREADS = 10
+        def test_function():
+            for _ in range(LOOPS):
+                m()
+        threads = [threading.Thread(target=test_function) for _ in range(THREADS)]
+        for thread in threads:
+            thread.start()
+        for thread in threads:
+            thread.join()
+
+        self.assertEqual(m.call_count, LOOPS * THREADS)
+
 
 if __name__ == "__main__":
     unittest.main()