I think this was asked and answered before but ... is not a small yield test an indication of greater sophistication than if they just lit off a Hiroshima-style nuke?
Getting the conventional implosion to concentrate the reacting mass as efficiently as possible is technically and mathematically difficult. It requires a precise timing by high-speed switches to ignite the conventional explosive around the reactive material, and a shaped arrangement of that charge in different thicknesses of different types of explosive, to precisely "focus" the imploding material on a small sphere at the core of the bomb.
Understand, as the nuclear reaction spikes, it opposes this inward pressure wave. Both neutrons and gamma rays released in the core at striking the infalling material and dumping their energy into it, slowing its collapse. The neutrons can travel farther into the material before hitting anything, since they do not react with the electron shells of the matter around the core, but only hit something when and if they hit an atomic nucleus.
John von Neumann did the math for the implosion lense back in the 1940s, and everyone else on earth, since, has cribbed his answers instead of working it out against for themselves. OK, a few US and Russian scientists working on fusion weapons were also competent to do it (Teller, Sakharov e.g.). But it is far from trivial.
Also understand that a simple gun-type bomb of the Hiroshima rather than the Nagasaki design can dispense with this step, but only by using a much larger amount of uranium instead of a smaller amount of plutonium. It is not possible to shrink a gun-type warhead for missile delivery. Those can't be made under 4 tons or so. All smaller deliverable warheads (by anything other than a large manned bomber I mean) rely on a plutonium implosion design and require mastering the implosion lense. It is easily the hardest single step in making a *deliverable* nuclear weapon.
I want to know exactly, what is a "few Kilotons". Also in answer to your question: I believe some people have said they are trying to get them small enough to fit on a missile and that the small explosions reflect that. A 4 KT bomb would destroy the centers of any large US city and kill thousands and maybe millions with loss of service and fall out(radation depends on how high they explode the bomb, ground bursts produce more radiation, air bursts less).
Tell the people in Hawaii or Alaska that a missile with a "few" kt is coming and not to worry and see what they say!!!