The best way to check a breaker is to remove the cover of the box, 2 to 4 screws, and test for power on the output side of the breaker. Black lead from the meter goes to the bus with the white wires, red lead goes to the screw on the breaker itself. Do not pull too hard on the breaker itself as the breaker usally is not held in by anything other that the cover you just removed. If you pull it can pop out
I would flip each on off and on with the meter probe on the output screw and see if it works as it should. as breakers get old they will cometimes fail, or get weak. If this is the problem take to bad one with you to HD or Lowes and you can get a new one for less than 10 bucks.