Parsed test spec with 2 sessions

starting permutation: w1_fetch w2_fetch w1_commit w2_commit
step w1_fetch: 
    SELECT payload::text
    FROM ulak.queue
    WHERE status = 'pending'
      AND (next_retry_at IS NULL OR next_retry_at <= NOW())
    ORDER BY id
    FOR UPDATE SKIP LOCKED;

payload        
---------------
{"vis": "now"} 
{"vis": "null"}
{"vis": "past"}
(3 rows)

step w2_fetch: 
    SELECT payload::text
    FROM ulak.queue
    WHERE status = 'pending'
      AND (next_retry_at IS NULL OR next_retry_at <= NOW())
    ORDER BY id
    FOR UPDATE SKIP LOCKED;

payload
-------
(0 rows)

step w1_commit: COMMIT;
step w2_commit: COMMIT;