It's always possible that something was not tested right, but if your friend knows what he's doing then hopefully he would know how to check these. I'm guessing that your PS4 is turning on then right back off since this is a common problem with them.
I don't know of a special way to test these PSU's. These power supply's are just a switch mode power supply. Anyone with some knowledge and experience of switch mode power supply's should be able to test them.
Normally when these PSU's go bad there is nothing that is burned...there is no way to tell what is wrong by looking at it you just have to test them.
One way to do a quick check is to put the PSU in the PS4 and turn on the PS4. If the blue light barely even blinks on or doesn't go on at all, then you likely have a problem with the power supply. If the blue light comes on for a few seconds and the fan starts to spin up then it turns off then you probable have some other problem.
I hope this helps.