Coil failure can be an expensive service as many shops recommend/require replacing all coils at the same time. Many times it is just a single coil that fails. I understand that some OBD readers can isolate an offending coil.
There is available a simple inductive coil tester: Waekon 76562 coil over plug quick probe at about $95. Sold both by Amazon and Lowes. This tester will pick up spark impulses while the vehicle is stationary. It does not work to test intermittent misfires under load unless the misfire can be replicated when the car is stationary.

 

Any decent OBD2 reader would pull a code, such as "Misfire Cylinder 4" and then all one would have to do is swap #4 and see if the fault followed the coil or stayed with the cylinder.

 

Ditto. Takes a couple minutes to swap them out once the intake tubing is out of the way. I picked up a full set of 8 coils for the wife's Explorer for under $20 from China. Been going strong that past four years...

 

Even without a scanner, with a V8 you can feel which side is misfiring and change them through trial and error,. Just a shame that changing them seems so much more difficult on an x150 than an x100

With my.old car I could change them all out in around 30 mins...and that included the plugs and the cost of my old were a mere £22 each for Lucas coils

 

How big a deal is it to change them?