Testing is something that very few do enough of and is very critical to a makers development. I think the tendency is to have the attitude of "out of sight, out of mind". The things unseen in the knife are the most important, but easiest to ignore.
In my opinion, it all boils down to dicipline. If a maker of any material object wants to set a high standard of quality and performance he has to perform his procedures with some degree of consistancy as well as insure that his procedures gives the best results possible. Most industries place a high degree of importance on testing. Any maker of bow or knife should too.
Even though a knife is just a material object, very often you will hear that it has "life" or a "heart" or "soul". I believe this is just a way of refering to the things about these inner qualities of a knife that are mostly unseen. These "things" that are important but somewhat mysterious. It's this mystery that needs to be cleared up by the maker for him to really make good knives. The only way to do this is to test. Even then, we might not be able to "see" with our eyes, but the results become manifest.
Now back to Chris's question. How do you test?