We determine the length of test drive by what the customer complaint is. Same with after repair test drive. Some just need to be driven a mile or two to confirm the repair, others need to be driven a few miles to complete the repair.
We dont drive the vehicle if it has no/expired plates. If the vehicle comes in with no fuel, it is not test driven. If it is necessary to test drive to diagnose or confirm repair, the customer is charged for the fuel. If the vehicle doesnt need to be driven or run very much, I tell the customer that they need to go to a gas station after they pick the vehicle up or to bring gas with them. Then I ask them not to bring the vehicle in with under 1/4 tank of fuel.