One thing about testing a regression test is that there's quite a bit of “hurry up and wait”—I add a check, run the test and wait (Regression tests are good for this as well) [1]. Then investigate the output and either make a note of a potential problem (either in the configuration of the test data or a possible bug in one of a number of components) or adjust the check (“hmmm … on second thought, it should really be this”) and rerun the test.
Fortunately, the regression test for “Project: Sippy-Cup [2]” (runs for maybe half an hour) isn't as long as the regression test for “Project: Wolowizard [3]” (about 4½ hours).