I usually test it by seeing what the voltage is at the battery running. It should usually be 14-14.5 or so but more then normal battery voltage at the least if the alternator is working.
Every time I've had a voltage regulator fail the lights would get brighter and dimmer as you're driving and speed up and slow down. I haven't had one that's caused a no charge but have had the plug or wiring st the plug anyway be bad.