Engine off, pump the brakes about 5 times,push down on the pedal and keep it there,start car, pedal should fall about 1 inch. If it does the booster is working. release pedal.
Engine running, pump the pedal about 5 times, the engine should not care a bit and continue to happily idle.Diaphragm is good.
From under the hood engine idling. Clamp the booster hose with a large enough plier to completely cut off the vacuum to the booster. The engine idle should not change one bit. Pump the pedal about 5 times.Release the clamp;engine idle should falter and recover to normal. Booster diaphragm is good .