Canonical promised that Mir would be available as default for the released of Ubuntu 13.10 (Saucy Salamander) and now the company is searching testers that are willing to improve the overall experience.
It's not uncommon for developers to ask for the community's help, but Canonical is usually doing this kind of testing in-house. Mir is proving to be quite a challenge and testers are needed to improve the displayer server.
“The Mir team is calling for a round of testing for Mir and multi-monitor support specifically starting today through August 28th. Help us during this round of testing to make sure Mir and features are thoroughly tested on as many devices as possible,” stated Canonical's Nicholas Skaggs.
A comprehensive Wiki page has been provided by the developers and users have been asked to report any results, good or bad.