*nuclear rant mode...on*
I believe they went ahead with the test in order to show the UN, and it's new South Korean President, that it doesn't give a shit about what the World, the West and the Chinese, who told them not to test, think.
They're going to keep jabbing away, pissing off the rest of the world, until they either get whatever it is they really want, or until someone shoves a boot in their ass and they calm down. I don't believe they are stupid enough to try to launch any nuclear payload anywhere, nor do they currently have the ability to do so, but I do believe they are like a spoiled child that wants to play with the big kids and gets all riled up when they won't play with him. The bigger picture is that the assholes now have the ability to set up shop and sell their limited quality nuclear devices to other non-nuclear countries that have a lot of oil $ and not much more sense than that of the North Korean leadership.
*nuclear rant mode...off*