Here's a man who should know what he's talking about: Siegfried S. Hecker was director of the Los Alamos National Laboratory from 1986 to 1997. In an FP article, What to expect from a North Korean nuclear test, he first of all looks at the technical stuff, and suggests that the most likely device to be tested is a highly enriched uranium (HEU)-fueled bomb, to a design originally used by Pakistan and supplied to the Koreans by A.Q. Khan in the early 1990s.
Then, on the political ramifications:
One of the most damaging results of another test will come from potential cooperation with Iran. Sharing Pyongyang's nuclear test experience with Tehran similarly to how it has shared missile technologies will greatly increase the Iranian nuclear threat. Iran now has the capacity to enrich uranium to weapons grade, although it has claimed to have enriched it only to lower levels for peaceful purposes. It would be very difficult for Iran to continue its peaceful nuclear façade if it tested to further its nuclear weapons capabilities. However, if Pyongyang were to involve Iran or share its testing experience, that would change the picture dramatically. Should Iran make the decision to build nuclear weapons, it is more likely to do so without necessarily testing its own device.
But perhaps the greatest impact of another North Korean nuclear test is that it will signal that the new regime, like its predecessors, has chosen bombs over electricity. Another nuclear test will make it impossible for the new South Korean government or the second Obama administration to look for resolution of long-standing enmities by focusing on issues beyond the nuclear dispute. Normalization of relations, a peace treaty, access to energy and economic opportunities -- those things that come from choosing electricity over bombs in the nuclear arena and have the potential of lifting the North Korean people out of poverty and hardship -- will be made much more difficult, if not impossible, for the next five years, if not longer.
The electricity outlook in North Korea is indeed, at present, not encouraging.