So lets say u smoked some weed not knowing it was laced and than sometime shortly after got stopped by the police and drug tested for whatever reason.

And they found whatever drug in your system and tried charging you with a felony for it. Do you think you would have a chance fighting it if you told them that you didn't know that the weed was laced until after you smoked it? They could still charge you for the weed of course but that's only a misdemeanor