IMHO, read the reviews but take them with a grain of salt. Test some on your own. I heard someone say in a video or review one time that it is so stupid to see so many "photographers" buy gear and sit at home doing tests on them all the time instead of actually using them. I kinda of agree, It all depends how picky you are. You cant satisfy everyone.
It's no more stupid than photographers who have no idea how their equipment performs or what they can expect from it under different conditions- let alone if the expensive lens they just purchased is out of alignment. You see a scene that needs about 35mm of coverage- you have a 35-70mm lens and a 20-35mm lens- which one do you use? If you've not tested both lenses how can you pick which one is the better choice?
Knowledge is power, knowledge comes from information. Without information, you can't gain knowledge. Information gathered under controlled circumstances is generally better information.
Perhaps it could be said that the photographer who's tested their equipment can afford to sit around because they don't need to spend as much time trying to get the shot...
Personally, I find that the more time I've spent doing photography, the less photographs I need to take to get my shot. I no longer feel the need to spend an extra half-hour taking an extra 500 images "just in case." Two or three shots of a subject is normally one or two too many.
YMMV, but I find that most people who ballyhoo testing tend to be the types that would benefit most from the discipline of doing so.
Ask yourself this question- why would manufacturers put focus adjustment into high-end professional cameras if they didn't expect (a) enough sample variance in lenses for it to be necessary and (b) enough photographers to test focus to actually use it?
As far as how much testing to do, I think it's the height of hubris to assume you know what someone else needs to do to get their comfort zone around their work. Heck, I've known photographers who've shot years of a single subject, which I'd find boring and mostly worthless, but they find satisfying.
Paul