Any easy way to test the CDI itself if those are all fine
If those test fine, it doesn't mean the CDI is bad. Still need to check the black/white wire running to the main switch that could have chafed and is grounding out against the chassis, the spark plug is deemed good and gap is correct, the spark plug boot is clean and not corroded, the battery is strong enough to spin the engine over fast enough so it can generate a spark, the stator wires are in good shape and the stator tests out (not saying you should test that now, just saying that's a piece of the CDI's puzzle), the spark plug was grounded properly during the test when checking for spark, etc.
It happens, but an overnight failure of a major electrical component seems too odd. To have it run without any symptoms, park it, then come back out 12 hours later and have nothing sounds like something is corroded/dirty, loose, chafed, dead/dying, etc.
Check the easy/cheap/free stuff, then double-check it: Multimetering the wiring, install new spark plug and gap it to spec (or just below spec), charge battery. CDI's and coils are non-returnable electrical parts so if you hope they fix your issue, then they don't, you can't return them to get your money back. Make sure you have checked all other options before throwing those parts at it.