The idle thought occurred to me that a possible test of a 6502-based board is to drive the address bus through all states. The usual solution is to strap a "NOP generator" somewhere, but it seems easier to just replace the 6502 with a test harness that drives the address lines. The purpose being to observe the address decoding circuitry on the board.
A 40 pin DIP board with a 16 bit counter connected to the clock, plus whatever is needed for the phase signals.
Does such a thing already exist?