Tear down the registered backend. Useful for tests that want to
verify no notifications are posted, or for app teardown. Also
resets the once-only warning flag so a subsequent missing-backend
call emits a fresh warning (otherwise tests that rely on the warn
being observable would only see it on the very first run).
Tear down the registered backend. Useful for tests that want to verify no notifications are posted, or for app teardown. Also resets the once-only warning flag so a subsequent missing-backend call emits a fresh warning (otherwise tests that rely on the warn being observable would only see it on the very first run).