Rarely happens, but sometimes.....
There are only a few failure modes with a coil. The Primary "shorts" or "opens"
The senondary shorts or opens.
You can use a meter to test it. There are 4 connections for the coil. One is B+ and the other 3 are for the primary of each coil set. Place a meter set to ohms on the smallest range. Put one lead on the B+ connection and the other wire to each of the other terminals. You should have all 3 readings very close, within an ohm or so. Probably about 5-12 ohm range.
The secondary side you can take the meter and plug it into each tower pair (they are 2 across) the reading will be a lot higher and should be pretty close to the same probably around 750- 1.5K ohms.
Symptoms would be missing on 2 cylinders all the time.
What is the problem?
Jeff