Since I just found it for another post ...
Here is a site with some links to various sub tests:
A frequency sweep from 10 Hz up to 200 Hz.
www.audiocheck.net
Just start the volume low and ease it up to make sure you don't get into a dangerous (to your equipment) situation before you understand what is happening!
Note: I have not yet spent time with these links, so am not vouching for the quality of the tests, but it looks pretty good as a "fat, dumb, and happy" approach that doesn't require a large learning curve to evaluate your system/subs!