There has been a lot of speculation over whether North Korea has nuclear weapons and now they are announcing that they plan on testing. I'm a software engineer and I know that no matter how meticulously you plan a piece of software, you do not know if it will work correctly until you start it up and more often than not, it does not work exactly the way you planned. I imagine any nuclear engineering involves a great deal of complexity and many places where a miscalculation could be made. It seems to me that having a nuclear weapon that does not work would be more than useless if actually launched, considering the retaliation would be devastating. My question is, is it possible for a country to build a nuclear weapon and have any confidence that it will actually work without testing it?