There are actually three 'coils' involved. The spark coil(hooked to the spark plug directly and fires the plug), the trigger coil/module(says "when" to fire), and the stator coil(makes all the bike's electrical power).
The stator is the most failure prone part. The manual should have a test procedure for it, i.e. a resistance value through it. That resistance value can be correct through the stator but the stator can still be bad. Usually though, you can identify a bad stator by looking for continuity to ground through the charge wires. Unplug the harness going to the stator(stator is under the flywheel). Don't confuse the stator with the pickup/trigger coil (next to but not under the flywheel). Using an ohm meter, put one lead on one of the two wires going to the stator, put the other on an engine ground. There should be no continuity( 'OL' or 0 on the meter). Keeping one lead on ground, switch the other lead to the second stator wire and check, there should be NO continuity there either. There should be continuity from wire to wire THROUGH the stator.
A stator will often show a 'no spark failure' that goes away when the bike cools off a few(or many) times before dying completely. Unfortunately a bad/broken wire will do the same.
The same goes for the trigger coil, it should NOT allow a ground path through either of its' wires.
Whichever one does is bad, replace it, or you may find an electrical shop who will rewind the stator, or use this opportunity to put lights on the bike and get a lighting coil/stator unit.
DO NOT overlook simple stuff like a crapped out kill switch, if you have to cut the wires leading to it and try the bike for spark with them 'open' and wired together.