import threading
import unittest.mock
m = unittest.mock.ThreadingMock()
LOOPS = 10_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()
assert m.call_count == LOOPS * THREADS, f"Expected {LOOPS * THREADS}, got {m.call_count}"

$ python3.14 python_mock_call_count_atomicity.py
Traceback (most recent call last):
  File "python_mock_call_count_atomicity.py", line 21, in <module>
    assert m.call_count == LOOPS * THREADS, f"Expected {LOOPS * THREADS}, got {m.call_count}"
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: Expected 100000, got 95507