If it's urine testing you can buy synthetic urine at most head shops or truck stops, even porn stores. They have a mouth wash for mouth swabbing. Depending on your weight marijuana can stay in system for 60 days, the fatter you are the longer it will remain.
Ya, even in legal states they will be testing for marijuana, almost every single employer whether government or private has to to test because their insurance companies force them to. Drug testing will only expand and be more consistent in the future, it's an easy way for employers to "weed" out(no pun intended) drug users who could be liabilities.
Captaincaveman has it right. Sorry for the rest of the assholes like giggles on here, seems they have more time to shoot their mouth then to grow or help others with problems.