From Halopedia, the Halo wiki
The primary purpose of the UNSC Operational Test and Evaluation Center is to quantify and reduce risks during the acquisition process for a system, by determining how well the systems perform when operated and maintained by military personnel in operational environments.
The UNSCOTEC is known to have carried out a test of the re-entry and combat capabilities of the Mark VI variant of MJOLNIR Powered Assault Armor, prior to John-117 being outfitted with it on Cairo Station. For the purpose of the test, the UNSCOTEC enlisted the help of Maria-062, another SPARTAN-II, to wear the armor during the combat and re-entry tests.
List of appearances