Since 1992 the US government has found no need to conduct nuclear tests, yet congress has failed to ratify the comprehensive nuclear test ban treaty (CTBT). Ratifying the treaty is a cheap and painless measure that will help keep nuclear weapons out of the hands of rogue nations and will make Americans safer.
For more information see:
http://www.ucsusa.org/assets/documents/nwgs/ctbt-fact-sheet.pdf