sources seem to indicate that this was a high altitude launch. If so it could be for a couple things
1. test reentry vehicle protection
2. dependability for high altitude nuke test.
Reuters quoting Japanese government that missile flew for 50 minutes and landed in their economic zone
https://twitter.com/Reuters/status/935593091909718016
......Within minutes of North Korea’s missile launch, South Korea fired its own missile launch in retaliation.
......Earlier today North Korea issued a sabre-rattling statement in a state-run propaganda newspaper:
The mouthpiece for Kim’s one-party government said:
“The army and people of the Democratic People’s Republic of Korea will surely accelerate the final victory in the standoff with the US.......The US is driving the situation on the Korean peninsula to the brink of war by mobilising huge aggression forces while tightening the sanctions upon the DPRK.”
So they’re hurting!