I have been working with many IC testers like proline and ABI8000 etc, I was writing programs to test various digital and analog ICs, I noted some programs in the library for testing microcontrollers and microprocessors from various manufacturers.
usually you plug the chip in the socket and press test, then you get a result pass or fail. I never dug through the code written in the library to see how they did it but I guess they simulate external ROM with a special program to do various tests.
Regards
Mahmood