The testing (some in Practical Sailor, some in a book-in-negotiation) was on the water with a load cell. All kinds of weather, shallow water, long fetch. Best way. I broke a 2000-pound load cell in light air when a wake hit with no snubber. I was the only person on the boat that noticed; the impact honestly didn't feel that hard, since it was against the mass of the boat. But it snapped a 1/4-inch shackle.
How do you choose the best length? Like many things, it is compromise and experience. We surveyed many cruisers and learned that nearly all failures were in short snubbers. We notice that past about 30-40 feet (anchor to attachment) returns diminished and the chance of snagging something on the bottom went up. Same with diameter; too big does not stretch, too small will fatigue.
Another interesting exercise has been backing against anchors using momentum and stretch (bump setting). Obviously, you can get some real forces that way, on the order of a real storm. Occupationally useful for boats with weak engines or non-functioning engines. The only way I can really bury my big Manson in fine sand. Not yet published.
