When making a facing movement at a spring switch, what condition warrants testing the switch?

When making a facing movement at a spring switch, it is crucial to test the switch when the signal indicates 'Stop.' This condition serves as a safety precaution, as it signifies that something may be amiss in the switching process or track ahead. Testing the switch ensures that it is properly aligned and functioning correctly before proceeding, helping to prevent potential accidents such as derailments or collisions.

In scenarios where the signal is green or indicates it's safe to proceed, testing the switch may not be necessary as it implies that the track is expected to be clear and the switch is in the correct position. However, encountering a 'Stop' signal raises a flag that the crew must not proceed blindly, making it imperative to verify the switch and the surrounding conditions first before making any movement.