"The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no warrants shall issue, but upon probable cause, supported by oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized."
Still looking for the words "drug test" in there. Funny thing, the courts haven't been able to find them, either. And they also don't skip over that silly adjective, "unreasonable", which kind of screws up your interpretation. They say you're wrong and I'm right. Go figure.