Cooperative Testing Initiative

The Cooperative Testing Initiative, or Co-op for short, is the separate game mode where two players can join up and take part in test chambers built specifically for cooperative play. The players take the form of either Atlas, the short and blue bot, or P-body, the thin and wiry bot. Each bot comes equipped with their own Handheld Portal Device with separate portal colors. The portals are capable of maintaining the flow of things, even if it enters a partners portal, which is essential during some test chambers. There are five test courses, each with several testing chambers within, which will test both players' ability to solve the different puzzles as they progress. Each chamber becomes much more harder than the last, with the final test taking place outside of the official Aperture testing facilities. In these tests, the players are then put to the test and must use every bit of knowledge earned about the previous tests in the final one. The last chambers of each course, excluding the fifth, the players are told to go out and locate a certain disk for the DVD player found at the end of the course. Once found and inserted within the device, the players are given a few lines from GLaDOS before exploding violently, as it's the only means of getting out of the test chamber. Upon completion, players are then returned to the Hub.

During the testing, GLaDOS will periodically chime in and say a few choice words, either to bemoan the players' progress or point out their tiny flaws. She even goes beyond to try and break their partnership by pointing fingers at one or the other. If the player stands within range of one of GLaDOS' monitoring cameras and perform a gesture, it will illicit a response from GLaDOS, depending on the gesture performed. Players do not have to fear death while testing, as it's commonplace in the machine world. If a player dies, the other player will be given an indication that the other has died and where they died. The dead player will then respawn moments later from the chute the Reassembly Machine sends them through, ready for a second try. The players have an infinite amount of lives, and GLaDOS will comment on every death that occurs with dry humor or irritability. As players progress, they will cross checkpoints that lead into the next part of the test chamber. The checkpoints will allow players who die to respawn at the checkpoint for shorter travel time to the next testing chamber.