Electrical wire colour code is only reliable if its practiced at the main DB first.

Test pen can't differentiate Earth vs Neutral.

Multimeter is the better tool.

E & L = 230VAC
E & N = As close to 0VAC as possible, 1-2VAC is fine. Anything higher indicates improper wiring/installation
L & N = 230VAC

Majority of electricians rely on test pen. The minorities don't bother to use one as they don't understand E & N difference.

Earth = 0 volts, dead zero, the more zeroes the better.

Neutral = Will have very low VAC reading, it is never 0 volts AC, 0.5VAC isnt zero volts. It can be high reading like 5 or 10 VAC which isn't good since it adds up to the AC phase.

Henceforth test pen is a quick and useless tool to tell apart Earth & Neutral. That is the only reason why some see no difference in wiring until the mains is switched on. The test pen will never light up on a Neutral since its so low voltage.

Also be mindful that the test pen will light up with relatively low voltage, ie 50VAC.

Do be cautious if you are not trained & experience in measuring live voltage.