Before going through the newly-opened doorway, place a blue portal on the ceiling directly above the energy pellet receptor. The switch opens a door at the opposite end of the hall that leads to a room with the high energy pellet needed to activate the receptor at the top of the stairs. Grab the weighted storage cube and backtrack down the stairs (they're mysteriously back) to place the cube on top of the red floor switch.
Drop into the orange portal from above the pit to fly through the blue portal and onto the mound with the storage cube. Next, place an orange portal in the bottom of the pit formed by the receding stairs. Place a blue portal at the top of the nearest wall that's facing the weighted storage cube. The storage cube is a bit out of reach, but you can grab it with a momentum jump. At the top of the stairs is a small room with a high energy pellet receptor and a weighted storage cube. For now, go left up the stairs (the stairs later recede into the floor, forming a pit).
Right away you spot a red floor switch as the testchamber branches both left and right.
