The test itself involves using a Wattbike, and holding a gradually increasing level of power for 3 minutes at a time...after a brief warm-up at 100 watts, I went through 12 steps, from 160 watts to 380 watts, and finished collapsing on the bike! That said, it's a far less brutal test than the alternative, which is a 20-minute sustained effort, as if you "guess" wrong on that, you tend to pop about two-thirds of the way through. Ken was on hand throughout the test, keeping an eye on everything, and in the later stages shouting encouragement...
The end results were pretty good, and a decent validation of my current fitness levels. My Threshold power is 323 watts, and recommended training zones pretty much in line with my current ones. This information will be fed into my training plan, and hopefully it can be used to get some more improvements in the months ahead (at some point I probably need to think about dropping a couple of kilos of weight as well, but I'll worry about that once winter is over...) I did a time-lapse of the entire process, which makes me look a little bit like Roadrunner!