Pretty simple stuff, you know if you failed. Simply tell them. I don't get why you wouldn't? When I was going through new hire training, I was talking to a pilot who was about to take his PC, He told me he was nervous because he does not do well on checkrides. Later in the conversation he stated that he failed, Private once, then passed, instrument twice, then passed, commercial once then passed. I believe there was another one as well. Also during training I know that this person did not pass the systems test on the first try, or stage checks, and I believe the oral as well, and he is flying around as we speak... I wish I could make this story up....

So easy a caveman can do it.