"Christian McArdle" wrote

No such thing as voltage flow. Step away from the crude tester. Someone
might get hurt.

It goes from the live of the "on" circuit, through an appliance to neutral
on the "on" circuit. This is connected directly to the neutral of the
"off"
............snip................

Thanks Christian

Just to put your mind at rest, the tester is a pukka mains voltage device
with LED voltage indicators and self test feature.
The word "crude" was used, perhaps incorrectly, to differentiate this from a
high spec multi-meter.

Phil