How can you test relay if good or bad?

To test a relay, first disconnect it from the circuit and use a multimeter to check for continuity across the relay's contacts when the coil is energized. If the multimeter shows continuity when power is applied to the coil, the relay is functioning properly. You can also listen for a clicking sound when the relay is energized, indicating that the contacts are closing. If there's no continuity or the clicking sound is absent, the relay is likely defective.