I've always done extended test rides (usually by encouragement of the shop). However, I would be willing to buy after a short test ride of a few miles.

No way in hell I'm buying without a test ride any more than I'd buy a car without a test drive. Yes, there are many variables such as proper fit, tires, and the like that make a huge difference. But you can rough fit close enough and make some educated guesses as what you like and what you don't.

Besides, the test ride is an important part of falling in love with the bike. I've never wondered if I had the right one.