There is an orange portal in the area above, so create a blue portal on a wall nearby and walk through to reach the upper area.
There is a pit in the middle of the room with a floor that you can shoot portals onto. Shoot a blue portal onto this floor and drop in. You will end up on the higher level.
In this area, there is a glass-enclosed area with a hole in the top, and there's a cube inside. Shoot a blue portal under the cube.
Now hop down to the lower area. Shoot a blue portal onto the floor in the pit, then pick up the cube and fall into the portal in the pit. You and the cube should end up near the exit door. Put the cube onto the red button and go through the door.
There is a second area to this testing chamber. There is a pit in the middle of the floor that already has an orange portal in it. Look to the left of the door that you came in through and you will see an angled wall. Shoot a blue portal onto it. Then drop into the pit and you will fly out of the angled wall.
Now look to the left of the entrance and you will see some white walls that go all the way up to the ceiling. Shoot a blue portal as high up as you can on this wall. Then go to where the cube is, just below the ledge that you're standing on. Pick it up and drop down to the lower area, then fall into the orange portal in the pit.
Take the cube into the little side room with the broken glass and put the cube onto the red button there. A floor near the exit door will be raised, and the exit itself will open. Leave the blue portal where you made it and drop into the pit once more. You should end up on the platform with the exit door. Go through and down to the elevator.