We all know that Apple had tried waterproof technology on iPhone 6 before it officially announced that iPhone 7 is water-resistant. This just got me to think that maybe Apple has always tested its innovative technologies in its current generations to test their features and then release the next generation full-fledged. Any similar cases in which Siri/FaceID/any innovative technologies were tested in earlier models and then later implemented in the next models? Or, in short, how does Apple test its new technologies? How does it make sure it's safe/legit before it actually implements in a new device?