That was just to put suspicion on Saul and get people to think he could be the mole. But at the end of that same episode Saul went back and took it again and passed it. He was really stressed out and worked up the first time he took it so his heartbeat and stuff was rising, he came back and took it again when he was calm and collected and then passed it.
Saul did pass but Brody passed as well but we know that he was lying and passed anyway, so why couldn't Saul do the same thing? I'm not just going to throw Saul being the mole out the window so quickly.