SIU finds drugs in your car, makes a deal to let you go for a deal to be an informant. No official paper work. Says if you don't honor they get warran

A special ops division pulls you over and finds paraphernalia in your car. He doesn't test it to prove its positive for drugs, but offers you a deal to exchange numbers and narc on a dealer later... Let's you go and does nothing officially on paper. He says if you don't meet your end of the bargain hell get a warrant and still arrest you... What rights do you have when everything was vagily verbal and they left you without testing the evidence on scene.