Israel
Israel probably got a nuclear weapon way back in 1967. The weapon assembled was probably crude and never got tested.
However, in 1979, Israel was believed to have conducted a test in the Indian Ocean in cooperation with South Africa.
Mordechai Vanunu, a technician who had photographs and detailed technical information on how to separate lithium-6, confirmed the advanced state of the Israeli nuclear weapon program in 1986.
Separating lithium-6 is a key step for the production of tritrium, which is essential in developing fusion-boosted fission bombs.