The Testing Floor is a floor at Lumon Industries below that of the Severed Floor, accessible by an elevator down a dark and narrow corridor off the main hallways. No details are known about activities on the Testing Floor. The floor is mentioned just once in season one, after Ms. Casey tells Mark S. she is “retiring,” which Mark interprets as Ms. Casey getting “fired.” Soon thereafter, Harmony Cobel, referring to Ms. Casey, tells Seth Milchick, “Take her back down to the testing floor, please.” Milchick then does so.

Irving Bailiff's outie obessively paints versions of the approach to the elevator that goes to the Testing Floor, even though viewers have been given no explanation as to how his outie (or even his innie) might have ever seen the corridor in question.