How do you guys test ignition coils?

I have followed the internet instructions from a search, but am not sure they are correct.

I tested for resistance on the primary and secondary circuits. On 4 coils, there was no resistance on the primaries. School solution says this makes the coils bad. I am a little reluctant to trash all four, because at least two were working before I started tearing things down.


1946 1-ton Panel
1952 1-ton Comml. W/Grain Body