I sometimes argue, that you cannot test software. You always test the whole stack: case, printed circuit board, power supply, firmware, gateware, cables!!!, connectors, chips, clock circuitry, reset and poweron magic, cpu and other controllers, and finally software too. It can take a long time to even consider that your stack is broken somewhere else. And always use sunscreen (and backup) :-)
as my knees get older, so does my distrust in all aging systems :-P