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