The following is based on developer test content cut from Fallout 3 and has not been confirmed by canon sources.
DLC05TestAlien is a test cell in Mothership Zeta that can only be accessed by using console commands. The console commands to enter the rooms in this cell are: COC <cell name>. As the rooms in this cell can only be accessed through the use of console commands, they also must be exited in this manner (i.e. COC DLC05EngineCore).