NKs first leader, Kim il-Sung was born on April 15, 1912 (same day the Titanic sank). That is the significance of the date this week. No surprise at all if they test a missile or a nuke on that date. The US has anticipated this for some time. The missile defense system was headed to Guam months ago.
As far as China goes they are far more concerned about a potential refugee crisis across their common border should things go really bad. NK is a big red spot on the ledger books, and China is decidedly pragmatic. There is no way that China backs NK with military force at the expense of SK, Japan, and the USA. They want stability.
And the fellow "communist" rhetoric is nonsense. China's relationship with Korea goes back two thousand years. China went to war with Soviet-client North Vietnam in 1979 and was never really all that close with the USSR, except out of necessity.