How do you test a light fixture or bare wires?
So you want to know how to test wires ?
1 - If its a hot wire, Put an ac volt meter on it,
it should read mains voltage with respect to neutral.
If you dont have a neutral,
use an extention lead to a known good outlet.
Work your way along the circuit from the start
and test all points along the way.
start at breaker,
check at switch,
check at outlet/fitting,
If all these points test hot, with respect to
a known good neutral,
then its time to check your neutral line.
Only now, you are checking with respect to a known good hot,
via an extention lead if needed.
Please be super careful,
take all the usual safety pre-cautions,