"The Run-In Test repeats the Start-Up Test and checks for intermittent problems that the short start-up test does not detect. The test will run continuously until it is manually stopped by pressing the esc key."--See:
http://h10025.www1.hp.com/ewfrf/wc/document?cc=us&lc=en&docname=c01443317#N2498
(click on the link 'Performing the diagnostic tests" towards the bottom...)