This is nothing new. The PRC have been testing ballistic missile from this Golf Class test submarine for decades. In the 1980s they built their first dedicated SLBM sub the Type 92 (Xia Class). In the last decade they have built the Type 094 (Jin Class) nuclear powered ballistic sub to field the JL-2 ballistic missile.
What is interesting is the history of this class of submarine.K129 which was a Golf class submarine sank and the accident being picked up with the SOSUS network. We recovered parts of the boat.