ok it depends mostly on who's administering the tests, and if you've smoked or taken something and what it is, the marijuana in a person’s body doesn't just run out, it depends on a vast majority of things, such as weight loss (as the chemical/ active ingredient is fat soluble) and also the amount that person has smoked over a period of the last few months, if your not going to pass the drugs test you have 2 options
1. get some clean piss, or a substitute.
2. drink so much water you just piss water at the test ( this is risky if you smoke a lot) plus most tests have a strip to confirm it is urine