Not just testing - line-by-line code review of the entire system by a panel of experts. Outside of aerospace/defence/nuclear this style of review is not very common.
I don't know about now, but software verification would also be used in consumer electronics.
Fixing a bug in 10,000 washing machine control boards is very expensive when it entails sending a technician to every house to replace the circuit board.
Yeah, I guess for devices that can't receive OTA updates that makes sense. Though I fear that segment of the market is rapidly shrinking - televisions have ubiquitous software update capabilities now, and even washing machines are increasingly internet connected.
We didn't apply anywhere near that kind of quality control to smartphones or VR headsets. Once users are trained to install OTA updates to fix issues, most of the impetus for extreme quality control outside of the bootloader->OTA update path is gone
