You beat my post. My thoughts exactly. Who ‘tests’ on the side of the road at night?
Those who can't operate in the light because their deeds are evil. Of course the scheme was designed to intimidate and/or dupe a sufficient % of drivers. They've been stopped. Their license plates identify them. They are aware that police depts. have a reputation for holding on to bad apples or for systemic corruption and lawlessness. They know that there is no such thing as driving away anonymously. Saying "No thank you" could mean subsequent tickets and fines for the slightest infractions, real or manufactured.
Manipulators exploit these types of perceptions and realities to encourage compliance. Legitimate information gathering does not require such sleezeball tactics. This one is so top-heavy on the plausible deniability "it was voluntary" cover that it falls over on itself.