This is a case where we basically did test it on everything! Because the emulation community maintains conformance tests with over 3k of golden instructions. (And this is why Opus was able to so effectively build it; it found the tests)

Yeah, but that still doesn’t mean there aren’t theoretical bugs. Testing every input would effectively mean testing every stimulus, which is combinatorially impossible. You might still have subtle timing bugs, bugs with very uncommon instruction sequences etc.

But my point was exactly that the (extremely vastly) smaller subset of tests that you performed is more than enough to proclaim a CPU to be “working”.