Less IO for your Java Unit Tests
eng.wealthfront.com
eng.wealthfront.com
I posit that this kind of tomfoolery is required because (in my experience) profiling tools are (1) expensive (2) hard to use (3) inaccurate [could be due to #2] or the combination of the preceding.
Also, my current employer's tests run in the order of magnitude of hours, and I doubt very seriously that they are I/O bound (or network bound) in the manner that this page discusses. But, again falling back on the "hard to know without tooling", I couldn't state with any confidence exactly what the problem is with the tests, so this may be a great start toward finding out.