I had exactly the same reservations, Orson. My version of TCD gives TESTAE as the plural. But...maybe if my answer is wrong, some kind soul will correct me. In terms of how the clue works, I don't see what else the answer can be.
Similarly, I thought that 16D was a little loose. My TCD refers to a man working on a ship, not the ship itself...didn't really want to gripe about it before, since the puzzle clearly has something about it...and you know that I'm not the critical sort...