As you go into the testing chamber, a cube will fall out of the chute up ahead and onto the floor down below. Create a blue portal on the wall down there or just make one under the cube, then pick up the cube and put it on the red button. Then go through the door to go directly to the next test chamber.
There are two red buttons here and you need to put a cube on each one to open the exit door. One of the cubes is up on the platform across from the orange portal, and the other cube is in the pit across from the exit door.
First, create a blue portal on a wall that you can walk through. Go through the blue portal to get onto the platform with the orange portal. Then create a blue portal on the wall next to the platform with the cube on it. Go through the orange portal to get the cube. Jump down and put the cube onto one of the red buttons.
Next, create a blue portal under the cube in the pit across from the exit door. The cube will end up on the platform with the orange portal next to it. Create a blue portal on a wall that you can walk through, then get the cube from the platform and put it on the other red button. Then go through the exit door.
An orange portal will appear on the ceiling above you. Create a blue portal on the wall and go through. You'll land on the glass, which will break and partially fall down. Walk up the glass and go to the next area.
You can go up the stairs if you want to see a drawing on the wall. Otherwise, go to the exit and into the elevator.