that works fine as long as you aren't in a nuclear missile silo.....
actually if you want a way to test a button, you need to switch the button out of the circuit it's in, and into a test circuit, then switch it back into the circuit the button activates....
many modern devices have a test mode where you can test the various buttons and controls, then switch the unit back to operating mode. the ability to put something into such a test mode and back to operating mode is usually implemented by a processor.