I'm under the suspicion of my son using of y son using mushrooms, and i'm not one to jump the gun, so will a standard drug test prove this theory?

Difficult: Hallucinogenic mushrooms contain the active compound psilocybin, which can be detected in urine and serum -- but not for long. Psilocybin is water soluble and would be gone within a few days of use. You'd need a specialized urine test looking for psilocybin; standard ones don't test for this compound. A specific urine test for this can usually detect mushroom use within the last 1-3 days.