North Korea
1945 was the first year that a Nuclear bomb was successfully tested then used in combat.
The first implosion-style nuclear device was tested on July 16, 1945, as part of the Trinity test in New Mexico, USA. This test marked the first successful detonation of a nuclear weapon.
In recent months both Iran and North Korea have been identified as potential nuclear threats. North Korea has successfully tested several nuclear devices. Iran is still developing the technology.
the USA in 1945
I guess it's Pakistan.
Every country in the world received some fallout while nuclear weapons were being tested above ground.
North Korea has successfully tested a number of nuclear explosives. It is still unclear though if they have weaponized them. It is probable that they have succeeded in weaponization.
Both US & UK.
The US tested nuclear weapons on its own territory including the deserts of the continental southwest US.
England tested its nuclear bombs at maralinga and woomera in south Australia
No one. The first nuclear device was not tested until July of 1945, and the first bomb was not produced (not used) until later that month.