Is there any way to be 100% sure without taking the alternator out or taking it to the stealer?

Reason I ask is because I dont read over 13.5 when engine is running using ac diagnostic...

http://www.ehow.com/how_4601849_verify-alternator-working.html

Also - I disconnected negative battery terminal while engine was running and engine didnt die.

http://www.ehow.com/how_4519042_check-vehicle-alternator.html

These facts seem to contradict each other to me.