Name of Failure:

test.asynchronous.test_discovery_and_monitoring.TestPoolManagement.test_pool_unpause failed in task test-standard-v8.0-python3.12-async-noauth-nossl-standalone on variant test-macos-arm64, with AssertionError: Didn't ever find 1 <class 'pymongo.monitoring.ServerHeartbeatFailedEvent'> event(s).

Link to task:

https://spruce.corp.mongodb.com/task/mongo_python_driver_test_macos_arm64_test_standard_v8.0_python3.12_async_noauth_nossl_standalone_0e99c4694626def98c7171a1e7e87b2bb7ca03dc_26_08_12_17_02_34/tests?execution=1

Context of when and why the failure occurred:

Long-standing flake, not a new regression. On test-standard-v8.0-python3.12-async-noauth-nossl-standalone / test-macos-arm64, the task's last 15 mainline runs (order 3141–3155, 2026-07-24 through 2026-08-13) show failures interleaved with passes (8 failed / 15 total), and the immediately preceding run (order 3154, revision 2d2daed7fe) passed. Reliability over the trailing 28 days (2026-07-17 to 2026-08-14) is 13 successes / 28 total runs. The test waits up to 10s for a ServerHeartbeatFailedEvent after injecting a failCommand on hello/legacy hello, and the event never arrives within the timeout on this run.

Stack trace:

[2026/08/13 06:35:09.740] FAILURE: AssertionError: Didn't ever find 1 <class 'pymongo.monitoring.ServerHeartbeatFailedEvent'> event(s) ()
...
[2026/08/13 06:35:09.740] async with self.fail_point(fail_hello):
[2026/08/13 06:35:09.740] >           await listener.async_wait_for_event(monitoring.ServerHeartbeatFailedEvent, 1)
[2026/08/13 06:35:09.740] test/asynchronous/test_discovery_and_monitoring.py:383: 
[2026/08/13 06:35:09.740] test/utils_shared.py:96: in async_wait_for_event
[2026/08/13 06:35:09.740]     await async_wait_until(
[2026/08/13 06:35:09.740] >               raise AssertionError("Didn't ever %s" % success_description)
[2026/08/13 06:35:09.740] E               AssertionError: Didn't ever find 1 <class 'pymongo.monitoring.ServerHeartbeatFailedEvent'> event(s)
[2026/08/13 06:35:09.740] test/asynchronous/utils.py:80: AssertionError