His policy likely did provide cover, it doesn't make any business sense for a motor trader or anyone connected to the motor trade not to have cover for test drives added to a trade policy when it costs very little....it also stops the vehicle being seized.

If he was allowing you to drive a vehicle that's not insured, that would leave the trader wide open to the offence of, allowing a person to drive with no insurance....which is the same penalty for driving with no insurance.

The best practice is to ask to see his policy. Anyone reasonable would allow you to see the policy with no questions asked....

When I sell cars, yes, i make sure they have their own insurance. I ask to see the email or certificate on there phone.