The Apple Reliability Labs are fascinating. At the time I visited they were had a room of rapid prototyping machines. They showed me the door of the room and a couple very old prototypes (looked like early ’90s) in a case outside and then moved on. That door didn’t even have a window in it.
The lab had large vibration tables, climate chambers (which cycled from 0% humidity at 0° to 100% humidity at 0° to 100% at 100° to 0% at 100°F over a week’s time), machines for testing keyboards, machines for testing thermal tolerances,IR testing, and mechanical failure testing (hinges and iMac display arms). There were unannounced products here and there covered in black shrouds so there was no chance of someone seeing something they shouldn’t.
There were some stories of presenting machines to guide Steve’s choice to the best option for Mac Pro cases, or product engineers assuring the tester than certain failures would not occur then having that exact failure occur on the vibration table.
There were some prototypes of released hardware around; the most interesting of which was multi-colored iMac cases (Flower Power era, not anything recent).