How to make sure the wire I used for my smart switch is neutral?

[Tmcdiscord]

I'm new to this forum, I live in Saudi Arabia. I just installed a smart light switch that requires a neutral line, as in this picture :



when I opened the switch light outlet I found a black wire capped inside and not used, I used a voltage detector on the black wire and there was no voltage. So I thought it is neutral.

I have also opened a 110V outlet to check the color code of the neutral wire and it was black.

The smart light switch have actually worked great. However, I dont wanna leave things to chance and I want to make sure that black wire is actually neutral. So to be certain I guess my question is, since my smart light switch worked, does that mean a 100% the black wire is neutral? Or is there some other configuration that can happen which make the smart switch work somehow without a neutral that might cause some danger to my house?

 

[littlespark]

I believe the black wire is indeed a neutral.
Partly because it wasn’t attached to the original switch, and partly because your smart switch is now actually working.

It is good to ask though.