How long is the longest train in the world?

According to Trains magazine, Canada's Quebec, North Shore and Labrador runs the longest trains in North America: 240-car ore trains carrying 32,000 tons. However that's topped by Brazil's Carajás railroad, owned by the mining company Vale S.A. which, according to Vale's Wikipedia page, regularly runs trains of 340 cars. That's a length of over 3.2 km. Longer trains have been known to run experimentally. In 1986, Russian railways ran a test train of 439 cars weighing 43,400 tonnes. It was 6.5 km long.