If Russia were to "test" a nuke, the isn't the protocol to announce it in advance? A random nuke going off, even in a remote, uninhabited area, would set alarms screaming all over the world.
That said, if you're going to announce it beforehand, you better pick one that actually works. For all we know, they might have already tried and failed!
Which I guess is another point - how remote is remote? A one or two kiloton device is comparatively small and Russia is a big place - full of areas that are barely inhabited and plenty of people without internet. Some satellites are designed to watch for this stuff, but if Putin sets one off without going public - just a quiet threat to governments - would NATO itself go public on it? It could cause a bit of a panic.