Just to add to Vinny's advice, as a quick check prior to shooting at a competition, I check the scope on very close targets, 15 yards usually. If I can lay pellet on pellet, on the crosshair at 15 yards then I know all is well.
Last weekend, just before my first GP in many years, my FTP took a slight knock to the barrel. Rather then risk it and hope, I shot three pellets at the closest target on the zero range and as they all landed on the crosshair, I knew I was OK.
"I'm your huckleberry, that's just my game"