A junior engineer, monitoring a hydraulic system, shouts "Abort! Abort!" believing a high-pressure line has ruptured, though no alarms have triggered. As the Certified Test Conductor, what is your immediate required action?

1. Ask the system engineer to verify the junior engineer's observation before acting.
2. Check the test procedure to see if this failure mode is a defined abort criterion.
3. Acknowledge the callout and immediately execute the Emergency Shutdown Procedure.
4. Tell the junior engineer to stand by while you attempt to visually confirm the rupture.