The change stream test runner behaves slightly different from how the change stream test readme dictates:
https://github.com/mongodb/specifications/blob/master/source/change-streams/tests/README.rst#spec-test-runner

The change stream test runner should use a separate client for operations and for the change stream to prevent the command monitoring events from intermixing. Right now, our tests pass because we allow only match a subset of events (for just this test runner) by setting command_monitoring_allow_subset in test_change_stream_spec_cb. If we adhere to the readme, we may be able to remove that flag (which complicates the matching logic, and has been a source of matching bugs before).