Testing UV-blocking of sunglasses

Do I remember correctly that you can test the UV-A and UV-B blocking abilities of sunglasses by looking at a blacklight through them? I tend not to blindly trust labels on $15 sunglasses.

That doesn’t sound right – you can’t see UV B anyway. A better test would be to place the sunglasses between a UV source and something that glows under UV – a blacklight poster, day-glo paint, a coating of sodium salicylate – and see if it stops glowing with the glasses in the way.

That might have been what I remembered. I knew the details were fuzzy, searched Google but nothing looked useful.