I agree, you need to find a shop that will allow a proper test ride. The distance isn't too critical, but set up a test that has hills, open flats, and some rough surface. Take every bike you test ride on the same route so you can compare the differences. Tell the bike shop where you are going, if they do not approve invite them to ride along. If they still don't approve, they are the wrong shop, and tell them so. If they are the only dealer of a brand you are interested, send an email to the company telling them that their dealer is not cooperating with a test ride, have the area rep set up a ride for you.
I've taken test rides as long as 50 miles, a good bike shop should work with you to make sure you get what you need. If they won't work with you, don't work with them.