The 'who watches the watchers' line lands. What I'd add is that tests-as-the-gate only works if they could have failed, and a suite written next to the feature tends to certify the behaviour that's there rather than the behaviour you wanted. The domain knowledge you mentioned is what closes that gap, someone who knows the intended outcome writes the assertion the code can genuinely fail. Agreed it's a separate skill set, and it's the one that decides whether a passing gate means anything at all.