The best test for a bad stator I have run across is to find the connector for the wiring coming out of the stator, There should be 3 wires. Disconnect the connector and start the bike, use the idle adjustment to set the idle at 2000 rpm. Test the wires with a meter set on AC voltage. Wire A to B, then B to C, and finally C to A. All three readings should be with in 1 volt of each other. If one is higher or lower than the others it would mean a bad stator. Open or shorted windings. The idle adjustment will hold the RPM stable and the out put of the stator near the middle of the stators range. With the connector disconnected you are only testing the stator and nothing else. The bike will run off just the battery while doing this test.
The regulator will take the AC to DC and should regulate it to near 14V DC with no accessory load on. With your meter on the battery after you start the bike you can check the voltage at the battery at idle and with the RPM raised slightly. Too low and the battery will not charge, too high and it will damage the battery. At idle with the cooling fans running the stator may not be able to keep up with the current draw and the voltage will drop to near or below 12V until the RPM is brought up.
With the 2 test above you will not have to wait for the bike to leave you stranded along the road to find out if the stator or regulator are bad.