Were this high school, the idea of a "Perpetual Testing Initiative" would not be met with open arms--even if it were free. However, when Valve announces said program for Portal 2, people get excited.
The next DLC for Portal 2 will be available on PC and Mac on May 8th, the company has announced.
The "PTI" is simply a new name for the in-game map editor that Valve has already announced. It will allow players to play, create, and share Portal 2 puzzles. Fans will be able to browse the Steam Workshop to not only find user-generated levels, but also vote on them.
Unfortunately, the initial release of the DLC will not include support for co-op puzzles. However, Valve is still working on adding that in the future.