I would think that the initial US interception attempt would originate from ship born anti-missile assets off the coast of NK. At the same time a massive counter attack originating from US ships, aircraft and submarines would immolate every identified military asset in that country leaving it a radio-active wasteland. In this 'hair-trigger' environment, a test firing could easily precipitate the deaths of millions of North and South Koreans if it is mistakenly construed by the American forces as an actual attack on the US.