I've run this idea past a few forums over the years, and it's never failed to rouse some strong opposition.
Here's a post I made back in May 2007 in a forum for guitar teachers. It was around that time I came up with the 4 note test. The student mentioned was likely my inspiration.
So, what do you think about the test, and this approach to improvement as a whole? And most importantly, are you improving at it?