Old joke
A factory worker is caught at the exit gate pushing a wheelbarrow full of scrap newspaper. The security guard looks through the newspaper and finds no auto parts, no valuable copper, nothing.
This happens repeatedly: every day he leaves with a wheelbarrow full of scrap newspaper, every day the security guard rifles through the paper and finds nothing of value. Finally the security guard asks him what the hell he's doing. "Stealing wheelbarrows, of course!"
With this in mind, I wonder if Kim is actually using his 'test' missiles to deposit something on the floor of the Sea of Japan. Is he preparing for a blockade with ship-detecting nuclear mines?