Flaky test failure in test_report_app_metadata

[adamchainz]

This test occasionally fails with an error on the line assert mock_send.call_count == 1 . The value is 3 rather than 1. Unfortunately I can't find any examples on GitHub Actions runs because I've hit "retry" on all of them, however whilst working yesterday I hit this flake on several runs.

I think the failure is due to the CoreAgentSocketThread continuing to run from a previous test, although the pytest fixture stop_and_empty_core_agent_socket should be stopping it between tests.