The Soviet Tzar Bomba in 1961 at a yield of about 52 megatons had the biggest blast.
The US Ivy Mike in 1952 was the largest bomb in size, it weighed 82 tons and occupied most of an island in Enewetak Atoll and vaporized the entire island leaving an underwater crater in its place.
1945
China's first nuclear test took place in 1964 and first hydrogen bomb test occurred in 1967.
July 16, 1945 was the first nuclear bomb test by the United States.
the UK did some of its nuclear weapon test shots there.
The Trinity Test was the first test of a nuclear device. The bomb detonated at the trinity test was an implosion-type plutonium bomb nicknamed 'the gadget' the bomb was the same type of bomb that was dropped on Nagasaki Japan.
october 2008
US
July 16, 1945
there were only test on nuclear bomb in facilities such as area 51.
The French military explode their nuclear test bomb codenamed Aldébaran in Mururoa, their first nuclear test in the Pacific.
The main difference is test devices often have no casing, but this may not be true as some tests were done with the full operational military bomb (e.g. Crossroads Able in 1946 was a test involving dropping a MK-III bomb identical to Fatman from a B-29 over Bikini Atoll).
It showed that the USSR had nuclear weapons.