In the scenario I'm hypothesizing, why would anyone need to "check" or "test" its work? What chess players are checking to make sure Stockfish made the "right" move? What determines whether or not it's "right" is if Stockfish made it.
Today I learned that AI advocates being overly optimistic about its trajectory is actually not a new phenomenon - it's been happening for more than twice my lifetime.
The fact that you gave me the "you just don't understand, you're not a chess grandmaster" emotional response helps indicate that I'm pretty much right on target with this one.
FWIW I have been engineering software for over 15 years.