Ant-Man will become one of The Avengers after he gets his own stand-alone film. The test footage was all CGI, and was used primarily to give the audience an idea about Ant-Man's size. There was no actor playing Ant-Man, and the film was not announced as one of the four films Marvel currently has in production. Those would be Iron Man 3, Thor 2, Captain America 2, and (the just minutes ago announced) animated adventure Guardians of the Galaxy.
The test footage was "completely unfinished" according to Edgar Wright. While it showed off Ant-Man in all his CGI glory, there was also a lot of blue screen and wirework. At this time, Edgar Wright does not have an announcement about who will, or possibly could, play Ant-Man.
There is no news on when the film will be released, or when it will even go into production. We'll have more from the Iron Man 3 panel as it continues.