It takes a PSU load tester which is rare to find as a PSU is cheaper. But let's find it so you know.
That's the usual "tester" but it only puts on a fraction of the load required to do a full up test. Not only that but you need more. Such as.
1. Full load (50% load is usually enough.)
2. Oscilloscope to see if the voltage is right and stable.
Here's a full article about such a setup. http://www.tomshardware.com/reviews/stress-test,1073.html
Now you know.