I had this happen to me (not in Texas, however). Was directed over to a road stop in a fast food restaurant parking lot by the police, though they said ‘we’re not detaining you, you can keep going if you want’. At first I had thought it was a DUI checkpoint.
IIRC, they offered me money to give a sample, and stressed that it was supposed to be anonymous. Needless to say I told them that I wasn’t giving out any bodily fluids that night (I think I said ‘That’s super weird and creepy, no thank you’) and just left.
