If you dont hear a word by Monday, then call your employer and ask for your "start date". The employers answer there would shed light on whether youve passed or if the employer had moved on to the next applicant for hire.
Never inquire about the test results! A person who is truly drug-free would never do this because, being drug-free, theres no reason to do so. Doing so will only make things look bad for you, particularly if you want to be viewed by the employer as a "drug-free" person.