Ever have a Cutco salesman come to your house?
One of the things they do, is have you go to your kitchen and get your sharpest knife... They then take out a hunk of rope... Not sure if it's hemp rope or what, but it's like the old school twisted fiber rope. But anyway, they like drag the knives across the rope and show you how well they cut through it ( usually about a 3/8ths to 1/2" thick rope ).
Arm shaving works...
but after a while, even us guys with harry arms run out of test material. For quick tests, i just use my thumb nail... back when I could see really well, I could easily look at the edge of a knife and see if there were dull spots... I can still see them if I look close through my progressive lenses... Too bad you didn't have like a macro lens, or a microscope to take photos with.