Before today,... North Korea had conducted four nuclear tests in the space of around a decade. For a summary of the timeline of the previous tests,... Oh Soo-young reports. Nuclear tests have been North Korea's go-to last resort when backed into a corner. Pyongyang's first test came on October 9th, 2006 in protest of the U.S. freezing North Korean assets held in a Macau-based bank. The U.S. Geological Service's detection of a four-point-three magnitude tremor at the Punggye-ri nuclear test site signaled North Korea's arrival as the world's eighth nuclear power.