The tests were conducted in the X-ray and Cryogenic Facility at the National Aeronautics and Space Administration's Marshall Space Flight Center in Huntsville, Ala.
"The (tests) performed here are crucial to the success of the program since they'll ensure the mirrors and components will be able to withstand the extreme cold temperatures of space," said Helen Cole, Marshall's project manager for the Webb Telescope.
The mirror segment is the first of 18 that will be joined to make a 21.3-foot hexagonal mirror. NASA said each segment will be subject to temperatures of minus 414 degrees Fahrenheit in a helium-cooled vacuum chamber.
Each segment will be polished to about 100 nanometers accuracy at room temperature and then cooled to the cryogenic temperatures. Engineers will measure the mirror's surface, creating a "hit map" of unexpected changes and then those areas will be polished to get the mirror to 20 nanometer accuracy -- a process NASA said will take months.
The James Webb Space Telescope is scheduled to be launched in 2013.