Car wont start ! Battery or Starter?

just got out of work and went to start the TL. Put the key in and all I hear is one click.

Headlights, radio, all lights still work.

I tried jumping it with a buddies car but still not starting. It sounds like the click is coming from the starter. I tried banging on it but nothin Still !

Would this be a dead battery? If so how do I test for that ? Or do I need a starter replacement?