On May 21 North Korea tested a ballistic missile to a range of 560km and an apogee of 500km, about the same performance characteristics of a Pukguksong-2 medium range ballistic test in February. Furthermore, a press statement from the Korean Central News Agency confirmed that the missile tested was a Pukguksong-2 MRBM. The press release stated that Kim Jong-un has ordered that the Pukguksong-2 be operationally deployed into the field. This is the first of the new range of missiles to move from research and development to operational deployment, a process one expects will continue.
The Pukguksong-2 is a solid fuelled road mobile missile, which gives North Korea a survivable nuclear capable missile for strategic contingencies in its vicinity. Just how far it would be able to reach beyond South Korea is a function of the mass of its nuclear warhead, which is not known but it is known that North Korea has been developing more compact warheads. Most likely the Pukguksong-2 puts South Korea and parts of Japan within range. The Pukguksong-2 is a land variant of the Pukguksong-2 sea launched ballistic missile.
This particular test likely did not have a light dummy warhead, that is a dummy warhead lighter than operational requirements. As the KCNA press release states,
The test-fire of Pukguksong-2 was aimed to finally verify all the technical indexes of the weapon system and thoroughly examine its adaptability under various battle conditions, before its deployment at military units for action
The natural talking point is what might this mean for a solid fuelled ICBM. Here we must be cautious. The most common solid fuels are ammonium perchlorate and aluminium, which are mixed and bound together. Solid fuels need to be produced in large amounts, by no means an easy task, and the mixture needs to be cast to precise geometries which affects fuel performance. Different geometries can impact the thrust achieved by a motor burning the same mixture. Developing high energy solid fuelled motors with specific impulses sufficient for an ICBM is a very difficult undertaking, more difficult than developing high energy liquid propellants for an ICBM, and a deployed solid fuelled MRBM does not mean that North Korea can use it as the basis for a solid fuelled ICBM any time soon.
The first visible sign of a solid fuelled ICBM most likely would be a static test of a powerful solid fuelled motor.