In the high reliability industry (airplane, automotive, etc) the customer specifies very extensive hardware testing, so you have to have it just to get the bid.
Hardware in the Loop (HIL) testing is probably what you mean, and it simply involves some USB hardware I/O connected to the I/O of your device, with software on the computer running tests against it. The developers, however, also build a cheaper (sub $1,000) tester that includes a bunch of USB I/O, A/D, PWM in/out, etc and either use scripting on the workstation, or purpose built HIL/SIL test software such as MxVDev. In the automotive industry we use $100,000 custom built testers for each new product to verify the hardware and software are operating correctly.
