They have lost their test site because they demonstrated thermonuclear capabilities. NK is a nice position with their nuclear program, because they demonstrated

They have lost their test site because they demonstrated thermonuclear capabilities. NK is a nice position with their nuclear program, because they demonstrated last year that they have the ability to set of a thermonuclear explosion and the ability the launch intercontinental missiles. From the point of view of nuclear strategy that is a win, because even if they have problems with reliability, nobody is gambling a major city on a 1 in 10-ish chance that the weapons work.