//JOBF     JOB ...
//STEP1    EXEC  PGM=...
//IFTEST6  IF    ¬ABEND THEN
//STEP2    EXEC  PGM=...
//STEP3    EXEC  PGM=...
//         ELSE
//STEP4    EXEC  PGM=...
//         ENDIF

The determination of which steps to run is made when the IF/THEN/ELSE/ENDIF statement construct is processed immediately after STEP1 executes. This determination is not subject to change based on the results of running steps after STEP1.

Thus, if STEP1 does not abend, even if STEP2 does, STEP3 (and not STEP4) still runs. If, however, STEP1 does abend, STEP4 is the next step to run, as prescribed by the ELSE clause.