I use a few methods, one being the "does it shave" method - and different parts of the body take different sharpness

The other is slice paper, but the trick here is a hold a 8.5x11 sheet by one corner, and slice, pulling the blade so that every part of the blade gets tested. If there is a dull spot, the paper rips instead of cutting. BTW if you want to test for REALLY sharp, get thin "tissue" paper. Not the stuff you blow your nose on, but the stuff they use to wrap clothes when they are putting them in a gift box. The thinner paper makes it harder. Old phone book paper is also good, nice and thin

I saw an interesting treatease (sp?) on the difference between Japaneese and "western" swords, and the person pointed out that western sword makers COULD make swords that could be made as sharp, but they had a serious problem agains plate mail and even chain mail. The HUGE problem (and the whole reason for the diferential hardening of a traditional "Eastern" sword) was that they were VERY high carbon, and the edge had a real tendency to chip. In fact, he pointed out that if you look at REAL "Samurai" swords, you will almost always find chipping on the edge. This hardness issue lead to a different style of actual use, instead of "hacking" at your opponent, you tended to make a slicing cut, and the whole technique taught to use the sword is to make the sword do a pulling/slicing cut, and to lessen the initial "impact" of the blade on the target