Well, if that is the only problem, they will rather just fix it there, or give you an advisory. They will only fail if there is a long list of things wrong with it, so either way, it won't matter ever so much. With most places if it fails and you return for the retest with X amount of days, they will retest free of charge.
Your pride and joy is an old car, hats off to you if it passes first time.
About from the headlight, is there anything else that it will fail on that you know of.