I've never encountered one of these personally, but my then-girlfriend who was a recent nursing school graduate looking for her first job ran into them and failed the first few of them. After reading about them online I'm convinced the only way for you to "pass" these tests is to be slightly psychopathic or to simply know the very flawed theory behind the tests and train yourself to take them in which case they of course test nothing but how good you are at adapting to flawed tests.
The specific test she kept running into was the "Unicru" one:
http://melbel.hubpages.com/hub/Unicru
I highly recommend anyone running into this problem with HR in their tech companies do what they can to FIRE HR. This kind of bullshit needs to be nipped in the bud if it threatens to take hold in our industry.