I need some info,
What kind of test?
Will they be sending it to the lab after initial results?
Government job?
Generally the thing you need to worry about is cannabis, as most everything else will be cleaned out of you in about a week, quicker depending on your antioxident / fluid intake and excersize
also certain over the counter drugs will cause a false positive (example: DXM [cough supressent] can false positive for PCP) at which point they will either send it in to the lab for a mass spec chroma (which will show exactly whats in your system, or they will deny you the job right there regardless if its a mistake.
Mass spec testing aint cheap..