Parsed test spec with 2 sessions starting permutation: listen begin check notify check step listen: LISTEN a; step begin: BEGIN; step check: SELECT pg_notification_queue_usage() > 0 AS nonzero; nonzero f step notify: SELECT count(pg_notify('a', s::text)) FROM generate_series(1, 1000) s; count 1000 step check: SELECT pg_notification_queue_usage() > 0 AS nonzero; nonzero t