I have never walked into a shop that would order an out of stock size for a test ride. The only condition I have ever seen for a special order is your purchase of said.
I have had shops check within their dealer network to see if any other shops in a semi local area, or even nationally actually had one listed but more often that is just a 'so you know' move indicating that you are welcome to take yourself there to try for the ride.
In the case of the shop that I dealt with and worked in for a short time:
We would let just about anyone that had an ID, and drove a car in take an escorted test ride out in our parking lot. In some cases we would have one of our fast techs take a bike out with people that just walked in, assuming they could provide the other requirements.
If you were a regular customer with a history for buying items from the shop, particularly (return customer) bike purchases we would allow a round the block test ride.
We never allowed test rides in inclement weather, wet parking lot, etc. If the ride was going to require more than a very basic wipedown (if that) then no ride. Our bikes needed to remain new looking.
With all this said, one of the other major influencers in this situation was the actual bike size. Our shop would get an allocation (of sorts) of all manner of sizes small, medium, and large. IMOE everything that was 56/58 seemed to sell faster than many of the other sizes. Our allocation almost never included a bike larger than a 58. In many cases manufacturers make a very limited number of bikes in that size. As mentioned in the first line, that situation leads to a rare instance that I can find a bike in my size, 58-61 depending on geometry.