The closed beta for Mirror's Edge: Catalyst will go live April 22 and last for five days, closed April 26. If you've been selected and you're a Mirror's Edge 'Frontrunner' (suitably dystopian speak for being signed up to the mailing list), you'll receive a code April 22. Those selected but not on the mailing list get in April 23. Unfortunately if you've yet to register for the beta, sign-ups are now closed.
Closed beta will feature a selection of main missions and side missions and all of the social play features. Those are a little different from the first Mirror's Edge's developer-specified time trials, so DICE has put together a video explaining it all.
To me it sounds part Battlelog and part Dark Souls. I have astoundingly little interest in a social profile, companion app or website, but I love the fact you can design 'dashes' on the move or drop beacons for others to try to find like Souls' soapstone messages. With robust anti-cheat, custom dashes could keep Catalyst alive long after its story is told. From his hands-on, Samuel has gone so far as to describe it as the game Mirror's Edge should have been.