Slick Willy ended nuclear testing in the early 1990s.
Running computer programs is simulation, not testing.
A nuclear weapons code is a set of equations, up to a million lines long, that describe the physical processes that occur in a nuclear explosion. A code, thus, becomes the principal tool for nuclear weapons designers as they seek to meet the specifications for each new weapon ordered by the military.They embody 50 years of American nuclear know-how.