Conversation so far:
where does north korea test its nuclear weapons
Punggye-ri Nuclear Test Site was the only known nuclear test site of North Korea.
Where does France test its nuclear weapons?
France's TN 75 first full-yield test was probably the 110 kt detonation on 1 October 1995 at Fangataufa.

Question: why are the tests done
Self-contained rewrite: why are nuclear weapons tests done