There are three tests required to properly test a stator, and all three must be done both when the engine is cold and fully warmed up. You only need a multimeter and location of your regulator/rectifier and stator plugs on the wiring harness. The first test is the AC voltage output across all phases at the regulator/rectifier plug. Disconnect the reg/rec, start the bike with a charged battery, and measure the voltage across all 2/3 phases at the engine RPM specified in your bike's service manual. The voltage should be above the minimum specified in the manual and even across all phases. If it isn't, or the output is below the minimum specified across all phases, your stator is faulty and needs replacing. The second test is resistance across the windings. Refer to your service manual for the location where the stator connects into the wiring harness. We are testing the stator side. The method is the same as the first, check the restistance across all three windings. Generally speaking you should get about 1ohm, but refer to your service manual. If there is no resistance you have a short, if there is high restistance you have an open circuit. Both require stator replacement. The third test is resistance from each winding to earth, either the negative battery terminal or the main earth on the engine/frame. Check the resistance from each winding to the battery negative/main earth. Anything less than infinite resistance indicates a short, requiring a replacement stator.