this is quite simple:
Make sure the battery is in good condition, fully charged. Set the meter on DC volts in the range of 10-20v, start engine and rev to ~4000rpm, volts should be approx 14+.
If this fails then:
Remove and check the pin connector between the alternator and r/r for any melted/over heated connections, if these are good..
set the meter on AC volts (50-100v), start engine and check volts between 1-2, 1-3,2-3 wires an about 4000 rpm, ya should get about 50-60v on all 3 readings.
if any are low the problem is with the stator, if all 3 readings are good the problem is with the r/r. doing a test on the r/r is a waste of time.
Also when/if replacing the stator its a good idea to hard wire the alternator to the r/r, eliminating a common problem of corrosion with the pin connectors.
luck