No undo in the elevator

A nice test pattern to apply while testing software, is to revert all changes performed on one object or more, either by sending the keys CTRL-Z as often as possible or by using any other provided cancel/revert/undo operation if it exists. An interesting observation for me still is the fact that until this day, I had never been in an elevator that provided the possibility to cancel your choice on pressed buttons... resulting in the experience of real "pain".