[CentOS] bash test ?

Wed Apr 19 05:50:29 UTC 2023
lejeczek <peljasz at yahoo.co.uk>

Hi guys.

I cannot wrap my hear around this:

-> $ unset _Val; test -z ${_Val}; echo $?
0
-> $ unset _Val; test -n ${_Val}; echo $?
0
-> $ _Val=some; test -n ${_Val}; echo $?
0

What is this!?
How should two different, opposite tests give the same result
Is there some bash option which affects that and if so, then 
what would be the purpose of such nonsense?

many thanks, L.