Shrooms cannot be tested for. You are essentially poisoning yourself, you can't test for that.
I don't mean poisoning yourself in a bad way either, i love shrooms.
Actually I think when the psiliocybin/Psiliocin get turned into a form of DMT and get completely metabolized by the body. I could be wrong but it is definitely something to consider.
Peace
It already is a form of DMT. Psilocin is 4-HO-DMT (4-hydroxy-dimethyltryptamine). So it could turn into another dimethyltryptamine or atleast another tryptamine.