There are a lot of little things that can cause ignition problems. A sloppy distributor shaft, an uneven beaker cam, cap body electrode clearance with the rotor, a cracked rotor or body, a bad condenser, and there are others. I've even heard of pop out switches with broken wire strands in the armored cable causing problems. All the components have to be checked. Luckily, there are't too many things to check with a simple system.
An ignition coil has to be tested with a type of tester that will prepare it for test with a warm up and it tests it a lot like it works in the system. This is what was used back in the day. It's a Sun model AA3693.
https://www.worthpoint.com/worthoped...s-station-coil
The only other way to test it is while it's running with an engine. The more modern units with the oscilloscope were also a good way to test them.