If Israel and South Africa have tested any nukes, they have not advertised this fact. There have been several incidents that seemed to point to such testing, but nothing, as far as I know, was publicly confirmed.

It should also be pointed out that if the U.S. has sensitive technology designed to detect such tests, the detection of Israeli or South African tests may well have been classified to conceal our detection capabilities. In other words, it seems quite plausible to me that our military could have detected such tests yet not released that information.

BTW, who has South Africa's warheads--if any--now?