Brian Holcombe
A couple of my fellow Japanese tool nuts think I'm quite full of it for this but I don't test edges. I guess so many find it hard to resist cutting a piece of paper or shaving their arm or whatnot. I've tried the hanging hair a few times to see if I could do it (sometimes if the edge is shallow enough) but beyond that I don't find the exercises very insightful.

I simply put the iron back in the plane and the shaving/surface finish tells me everything I need to know about the edge.

I do, however, look at the edge prior to reinstalling and feel for a burr. If the edge is not clean or the burr not removed then I did my job poorly and should start over.

I look for the right reflection of light to show me a clean edge, perfectly straight and without undulations.

If lines, even very faint lines, show in your finish then you didn't do a good job or your edge has worn away quickly (likely because you didn't do a good job). A plane should leave a completely clean, bright finish that exceeds that of sander, if it does not, then your iron is not to its full potential.