One way to check your servos quickly is to place a resistive load on the control surface...

e.g. you push back with your hand... against the surface movement to a small degree while moving the surface.

As you move the surface while resisting it's motion, look for any movement which is dissimiliar or causes the surfaces to act in a racheting manner. This represents a broken or worn gear on the servo or a problem with the sensor.

It's not an all encompassing test, as the device which Bruce listed, but it sure beats not testing.