Three laboratories in the Denver area are handling the bulk of testing for safety and potency of recreational marijuana in Colorado. State law requires manufacturers of edibles like marijuana-infused brownies, to have their products tested for potency. And, growers of marijuana plants are subject to testing too. Denver-based journalist Nelson Harvey visited the labs and wrote a story for the Aspen Business Journal. Aspen Public Radio's Marci Krivonen spoke with him and asked how scientists are doing such tests.