If the alternator is bad you'll know it because the battery will go dead in a couple of days of driving.

If you have a Voltmeter, measure the voltage across the battery. Should be at least 12.0 volts.

Start the car and turn on the headlights with brights.
Mearure the voltage across the battery. Should be .8 to 1.5 volts higher than the first measurement.

JV