Is there any way to test the regulator without the proper power coming in?
If fallowed this flow chart and made it down to the bottom where we tested AC volts from the stator.
http://www.electrosport.com/media/pdf/fault-finding-diagram.pdf
Not really any way of testing it out of the system. Unfortunately with some electrical components the diagnosis process is testing all of the components that have specifications and can be tested and when they test good you have to go by your gut on the last couple.
Test the stator for AC output and then after the rectifier/regulator you should see DC volts and within the 13.8-14.5 range. The rectifier part is what converts from the stator AC output to DC for charging the battery and lighting/accessories and the regulator portion is what opens and closes to maintain the charging voltage range.
One way to assist in protecting the stator on any motorcycle is if the battery is dead or near dear use a stand alone battery charger to actually charge the battery. Don't jump start a bike and then rely on the charging system to charge the battery. The charging system is merely there to "replenish" the current used from the battery to run the bike and accessories, not to charge a dis-charged battery. This heavily taxes a stator and creates a lot of heat which can damage the stator as well as other charging system components.
Personally, I feel the say way about automotive alternators, don't use them to charge a dis-charged battery, just to replenish the power consumed during normal use. Anything more a person should use an actual battery charger.
Hope that helps.
Mike.