Or test with no load using a multimeter. Set the multimeter for continuity or resistance (Ohms). Check for continuity between the two big threaded terminals. You should find infinite resistance (open) with no power supplied. Now connect a battery charger to your solenoid, black/ground cable to the solenoid mounting foot, red/hot lead to the solenoid's spade terminal. You should hear a click when the battery charger is connected and the solenoid is likely to jump a bit. With the solenoid powered by the battery charger, use the multimeter again. You should find continuity (very low resistance) between the two threaded solenoid terminals.
Testing with a load like the headlight suggested above is better but the multimeter is an adequate test just to confirm the contacts are moving and closing.