The Divine Strake test that the United States is preparing to conduct at the Nevada test site will, after all, be a simulation of a nuclear explosion. Hans Kristensen has the story and a very good description of the upcoming experiment. In which he mentions the Minor Scale event in 1985, which "detonated 4,744 tons of high explosives on the ground, the largest such event ever conducted." I'm wondering if it is indeed the largest.
In 1985-1986, when the Soviet Union was observing a moratorium on nuclear tests, it conducted a test that detonated about 5,000 tonnes of high explosive at the Semipalatinsk test site. Details are scarce and my sources are not exactly reliable, but the test was reportedly known as "Shagan" and it was conducted to test effects of airblast on military equipment. Later, in 1987, a similar but smaller-scale experiment, known as "Morskoy Shagan" ("Naval Shagan"), was conducted at Novaya Zemlya. "Argon-85" was also mentioned as the name of one of these tests, but it is not quite clear of which one.