Just yesterday I had the cylinder 1 coil pack go out. The mechanic replaced with new and all okay. After a few hours, check engine light comes on and poor performance. I checked the plug that goes to the coil pace and it's broken inside, so I will fix. But the errors I got today are:

P0302 - Cyl 2 misfire
91313 powertrain (camshaft position plausibility)

Does this mean that cylinder two now is bad?

 

I is not unheard of the packs starting to go out all around the same time. That quick in your case is really fast but many here will say just do them all if they start going.

 

Is there any way to check the coils to see if they're good or not? How do coils fail?

 

if I understand right, swap out the coil for the one on the other side, the code should follow the bad one to where you put it in on the other side of the car.

 

There are coil testers. I'd buy a new coil to use as a spare, though.