Its hard to say, generally it will pass out of your system after a four day period (if the test is using urine) if you are a occasional smoker.However a multitude of factors depend on this (the research conducted used a Mexican strain of cannabis with a THC average value of 7%) the strength of the cannabis consumed, body fat,diet (consuming foods high in fats, does not aid the cause of passing a drug test) and how active you are (how often do you exercise). The actual drug test used plays a huge role as well, urine tests is the most common.But if any other test is used (eg. hair or blood ect..) the chances of being clean are slim.There are theories that consuming large amount of zinc hours before can give your urine a false reading of negative, however I doubt this is one hundred percent true or even works.
Hope this helps.