I've had a job for three years and havent been drug tested. what are the chances of getting one?

unless they change company policy, your not getting tested. Most companys test ever 4 to 5 months randomly, 3 years is very long time. And most places that drug test or coorperations such as buisnesses or more perminant position jobs. A seasonal job at an amusment park is less likely to test, if at all.