Voltage Regulator Testing?

For the future, a cigarette lighter voltmeter is good for diagnostics while driving, to help insure you aren't stranded on long trips. I use in all my cars. $15 Amazon, $5 HF. You should see ~14.3 V on the highway. I also have a Black & Decker charger with an "alternator test" button. I think it simply looks for a pulsing sine wave that indicates "alternator alive on the wire", so is just a screening tool.

Unlikely your Vreg is bad. More likely is wiring and connections. One common problem is that the case of the Vreg doesn't have a good ground to the body (thru mounting screw). I use a separate ground jumper. A multimeter can check all those things, looking for unwarranted voltage drops.