Whether there was enough in the text messages would have to rise to the level of "probable cause" for them to get a search warrant for your home. Talking/texting about getting high isn't enough, but if you talk about your stash that may be a different story. You do not have to and should not consent to a search in the unlikely event the police show up without a warrant. If you've got something you don't want to be caught with, get rid of it. For them to make you take a drug test (as opposed to a breathalyzer on a MIP case) they would have to basically stop you while driving on "reasonable suspicion" of operating a motor vehicle under the influence. Your friend is in a different situation because, as you say, he is already on probation so a different set of rules apply to him.