I don't work on the machines but I can provide you an example on why this wouldn't even work for simple machines like CNC machines. You could tell the machine for instance to move the drill out of boundaries, too hard, run it into a wall... All things that you can't catch with a software only unit test because the machine you're sending commands to doesn't really have any idea what else is going on in the space within it. So you can give it commands which are fine software wise but once they reach the real world, they can break stuffm