My apologies, I had thought that the instructions on the linked site were more detailed.
In your position, I would come up with a way to make it crash (rember seems reliable) then ask the Apple store if they'll test with different memory while running whatever that is.
If you want to try the AHT yourself & don't have the original discs (Apple will supply them for about $20 if you telephone them with the serial number) :
You should have a current backup in any case, but make extra sure before doing this, although it should not affect your system.
Open Terminal & paste in the following line, then press enter
defaults write com.apple.finder AppleShowAllFiles YES; killall Finder
Finder will relaunch & you may notice that some extra files are visible : that's normal.
Open the disk image that you downloaded, and navigate down to /System/Library/CoreServices/.diagnostics then select the .diagnostics folder, as shown below
Now open a new Finder window (Command N : leave the first as it is), then use Finder - Go menu - Go to Folder
Paste in the following line & press enter.
You should now have 2 Finder windows, one showing the AHTBTwo that you downloaded, with .diagnostics selected; one showing the /Coreservices folder on your startup drive.
Drag the .diagnostics folder onto the Coreservices window (not any sub-folder) & authenticate with an admin name/password when required to. There should now be a .diagnostics folder shown in both.
If you now restart your Mac, then hold the D key when you hear the chime; the AHT should start.
To return Finder to the normal mode where invisible files are not shown : open terminal again
& paste the following line, then press enter.
defaults write com.apple.finder AppleShowAllFiles NO; killall Finder