The best way to check it is to use it. Does it look fine - any marks on the lens surfaces? Also look inside the lens from both ends. Try the zoom and focus mechanisms and make sure they respond within expectations, that they don't make any funny noises.
Finally there are test shots to make sure there are no other flaws that may not be obvious. Test at a selection of focal lengths, at least at each end and one in between. Also vary the aperture, say from minimum f value at each length, and also f/8. Be careful not to induce too much camera shake when taking test shots. You might also want to try different focus distances as performance can vary with that. Just the extremes will do, something close (in same room) and something far (on horizon). All that remains is to look at the images and make sure they are within expectations, which is hard if you don't have something to compare it to. Remember it is a budget lens, so don't set expectations too high.
_________________Canon DSLRs: 7D, 5D2, 1D, 600D, 450D full spectrum, 300D IR mod
Lenses: EF 35/2, 50/1.8, 85/1.8, 135/2+SF, 28-80 V, 70-300L, 100-400L, TS-E 24/3.5L, MP-E 65, EF-S 15-85 IS
3rd party: Zeiss 2/50 makro, Samyang 8mm fisheye, Sigma 150 macro, 120-300 f/2.8 OS, Celestron 1325/13
Tinies: Sony HX9V.