NK does not need to test weapons, just as US does not today: weapons are computer-tested. NK stopping tests means nothing because we cannot see their computers. As w USSR, no agreement w/ it was ever truly honored anyway, just as NK keeps violating every agreement it makes.
Very incorrect that Gobechev didn't negotiate w Reagan; he very much did, because G understood USSR was bankrupt, had to come to table to implore US to stop arming, because USSR could not compete militarily w/ idiot Star Wars and stay alive economically. When that failed because Reagan didn't cave, USSR imploded shortly after during Bush's term in 89-91.
While I'd like to think negotiating works and it's vital important to keep doors open, it's been tried w NK, and will not work. There are plenty of photos of the late father smiling: current smiler is propaganda to US to believe this is a sea change.
The world is a dangerous place: our hopes and good intentions will not work here. NK is a figure head and military is in charge now.
Carry a big stick but talk softly...