Did you know that your Mac may have come with a pre-installed diagnostic test? Back in the days, you had to boot from the Apple Hardware Test disc that came with your Mac. For the past year or two, Apple has pre-installed these tests so you can run them without a disc.
Wondering if your Mac has a diagnostic test built-in? You could always just try booting up your machine while holding the “D” key, but if you’re having other hardware/software issues, this may not be successful even if the test is built in. Well, I just stumbled upon another way to check if your Mac came with a pre-installed hardware test:
1) Show invisible files in Finder (Onyx can do this but I prefer the free little app Invisibles).
2) In Finder, navigate to “Macintosh HD/System/Library/CoreServices”
3) If you see a hidden folder called “.diagnostic” (I think that’s the name, it’s “.diag[something]) then you have a built in test. If you don’t see “.diagXXXX” then you’ll have to boot from the Apple Hardware Test disc that came with your computer.
Next time I get a Mac with a built-in AHT I’ll re-post the exact name of the folder to look for.