Checking Lens Function

I found a Sigma 17-50 2.8 OS lens on Craigslist and am going to check it out today. Is there anything I should do to verify that it is ok? I thought I'd just slap it on my T2i and snap a few photos and then look at them on the back display to make sure they are in focus but other than that I don't know what to look out for...

-AF working
-OS working
-Focus ring smooth
-Zoom ring smooth
-Optics condition up to your standards
-Contacts in good condition
-screw in filter threads good

Make sure you zoom in on the pic on your screen, that little screen can be really misleading if you view the entire picture on it and don't zoom in looking for fine detail.

Prob too late to comment now. With this lens, the easiest way to check OS function is to put camera in Video and switch OS off / on. You will see the difference right away (if it's working). To check focus, use the lens wide open and zoom on some contrasty text at an angle, see if the letters you zoomed on are sharper than other, to make sure there's no front or rear focusing. I would also put camera in Servo AF mode and see if lens zooms automatically.

Congrats if you get this lens and it's a good copy. I love mine.