I tried to give it a piece of ~200 lines of JS I was positive there was an error in, and it tried to gaslight me into thinking there wasn't any... I tried everything, pointed it specifically to suspicious bits, asked for breakdowns, assertions, test cases... which it then promptly copy-pasted to me straight from my own code... Took me a few hours to find, but there was, in fact, a rookie mistake in it, just hard to spot at a glance.