Probably not. You'd need to remove and possibly dissassemble it. Common indications are excessive wear on the sprags that you can see on their bearing surfaces once they are out and a broken cage that holds the sprags. You might be able to see the cage with it together. You can't see the sprage bearing surfaces with the unit together, and once it comes apart it's tough to line up and get back together. Very tight tolerances.
The best way to tell if it's shot: Make sure your battery is fully charged and in good condition. It should read about 12.5V with no load and should not go much below 10V when starting the bike. If your battery is good try turning off or disconnecting the headlight and starting the bike. If it slips, it needs replacement.
A weak battery can mimic the symptoms of a bad sprag because there isn't enough power to get strong, solid engagement.
Scott