Anyways, the great thing about asynchronous ExUnit tests is that when you have CPU intensive tasks that run only on one core they can be parallelized automatically. I'm currently testing a bunch of things that basically call various ImageMagick commands (not the fastest) -- a test, when run in isolation takes about 0.5s to run, but the whole test suite (about 15 tests now, some faster than other) takes 0.8 seconds. :)