Hahaha most of these people are clueless.... you have 5 weeks. I smoked like 2 times a day for about 2 years then had to stop for some drug tests and was completely clean after 21 days. You are scared about a drug test that is about 35 days away and you are smoking 1 time.
Assuming you are clean right now (just by the way you are asking this question), You will be clean again like 3 days tops after you smoke. You have nothing to worry about....