Comment by mhh__

Details are obviously scarce but computers are pretty much the number 1 reason weapons testing isn't particularly necessary any more.

That's true, but it really applies only if you have access to historical nuclear test data. The computer simulations are reportedly parameterized using empirical factors that aren't openly published and aren't available to additional nuclear aspirants unless they run tests of their own. The alternative, if you don't have test data and don't want to test, is to build very simple, conservative bomb designs like the US did with the Little Boy gun-type uranium bomb. It wasn't tested before it was dropped on Hiroshima. That's also the kind of design South Africa used for its secret nuclear weapons program:

https://en.wikipedia.org/wiki/South_Africa_and_weapons_of_ma...