It’ll likely be a near fizzle... I believe modern seismology and satellite radiation sensors can determine a great deal about what was tested in such tests nowadays. I’d say, why try to stop them. When things go awry, that’s more scientists who will be fired, if not worse. Pretty soon there will be nobody left there to create these bombs any more.
A HEU gun-type bomb is much more idiot-proof than a plutonium implosion device; if they test I bet this one is pretty successful with a 15-20 kt yield, similar to the Hiroshima/Nagasaki bombs.
That said the HEU device could be an implosion device as well; the experience with their two previous tests would be applicable to such a device (which is more efficient than a gun) and I still think they are likely to have a more successful test this time.