Once the hood is open, the test takes just a minute or two. By the time the mechanic finds your car, drives it into the shop, does the test, writes up what he found on the repair order, and drives the car back outside, it's easy to use up a half hour.
At the very nice family-owned Chrysler dealership I used to work for, we had the owner's blessings to do this for free on our lunch hour, as a customer goodwill gesture. It doesn't cost the shop any resources other than the mechanic's time.
Tuesday, September 29th, 2015 AT 7:50 PM