From their perspective, what are you going to do?

Say you implemented a new function and missed some clear edge cases in the new tests. Or perhaps there's no tests written at all, because it was half-assed.

You will have to speak up in a peer review. I'd speak up just to have it written down. Perhaps you just forgot to `git add` that part, I don't know. It'd be professional negligence not to at least bring it up! If your reply is then, 'I'm aware, and didn't do this for reason X', that's perfectly fine, if reason X is at least slightly better than couldn't be arsed.