You're assuming the car doesn't also cheat on the "make install" test. How do we know the car isn't programmed to secretly leave the cheating software intact?

You're assuming the car doesn't also cheat on the "make install" test. How do we know the car isn't programmed to secretly leave the cheating software intact? Whatever extra layers of software verification we attempt to throw at the problem can be defeated by extra layers of deception from the manufacturer.