Really? Halfords won't let you have a test ride??? That's crazy.
Halfords seem to be a little bit confused at the moment. They do seem to be trying to get better, if you look at their website they are selling a lot more high end components, their bike range is certainly expanding.
When you go into a shop, the staff always seem nice enough, and willing to help, although I find that all too often they are unable to help. I'm not sure if it is because their product range is too diverse, or the staff aren't properly trained, but something just isn't there.
But, as a handy place to go when you need X* in a hurry it certainly is, especially out of town when you only have local bike shops in the area, that are all inevitably shut on a Sunday, which is always when I discover I need X when doing the bike, and Halfords most of the time do stock X.
*X = Whatever thingamajiggy you happen to need to make your bike operable again for the Monday commute.