You want to cock the hammer. Put the safety on. Pull the trigger.
Now, here's the real test. Keep the pistol cocked. Put the pistol up to your ear. Pull the hammer back slowly (past the currently cocked position). Do you hear a tiny "click"? If so, that is your sear springing back against the hammer hooks as you relieve tension on it by over-cocking, and that is BAD. There should be NO sear movement at all (no "click") when you pull back on the cocked hammer with the safety on.
If you do hear a tiny "click", time to buy a new thumb safety - or weld up the lug on your current one.