Good question. I think the probation officer can set conditions (approved by the judge) that include drug testing. I don't know what they test for (in NY they no longer test for cannabis). If TFG is allowed to serve his probation in his Florida dump, unless someone watches closely he could easily have someone else pee for him.
Recall that TFG also said he wanted Biden drug screened before their upcoming debates. Turn around is fair play, Donny.