You're exagerating, there is a clear increase in the pace of tests over the last two years. One each in 2014 and 2015, 5 in 2016 and 12 so far this year. But this also mean that one extra test doesn't change much.
At this point, the one thing that could cause someone to overreact is NK displaying a capacity to send a nuke via ICBM.
... isn't the whole reason people have been getting increasingly tetchy about the last couple (including the latest) specifically because they've been displaying greater apparent launch capability, relative to earlier tests? Iirc (I just woke up, mind, so I'm pretty definitely forgetting details, here) either this latest one or the one before displayed capability fairly conclusively indicative of being able to hit LA for the first time, or somethin' along those lines.
One extra test can change quite a lot if that one extra test is different from the ones before, heh. There's also, as y'note, the increase in frequency. Which I can kinda' understand, either 'cause they're getting close or 'cause one of their primary antagonistic entities (the US) ended up electing someone persistently inconclusive about how willing to nuke someone they are. Hand in hand with the political party that's been willing to include glassing other countries in their rhetoric without much or any censure gaining enough institutional control to conceptually make an offensive strike possible.
Add on that one of the major nuclear powers (russia) also violated a non-proliferation treaty (ukraine's you-no-invade-we-no-build-nuke thing) in the last few years, and you got some pretty fresh incentives to get stuff able to get in the air.
One of those cases where as sketchy as all hell as I am about NK being a nuclear power, at the same time I have trouble blaming pretty much fucking anyone for wanting the capability and the potential deterrence it brings to the table, right now.