Slightly off the immediate subject, some aircraft, such as the Seneca, have vane-type stall warners that can't be tested on the ground unless the landing gear squat switch is manually operated to give a 'weight off' signal. Annoying as it has two vanes, one dependant on the flap position. Most crew are probably not aware of this, so there is always the possibility of a malfunctioning stall warning system not being detected. Bad design fault in my opinion.