Mike J. put together a good page on test riding a road bike at:
How to evaluate a road bike on a test ride | Almost-Daily Diary
Now I know this is oriented towards op bar bikes, but if you're planning to ride a metric I think the same basics apply.
I read an earlier version of this page before I bought my last bike shop bike. I left my daughter in the store and went for a 2-3 mile ride on each bike (she's almost as good as a credit card, apparently). I've done a couple test rides at a bike shop where they know me, and they were OK with me riding through the neighborhood behind the shop.
Insist on getting a decently long test ride and a good fit. Those are part of why you're often advised to buy the bike shop first, then the actual bike.