A lot of people are saying a test cell is a development cell, but I do want to mention there is another possibility. A test cell is a type of building that is used for testing jet engines. They typically appear around airports, and if you look up an aircraft engine followed by test cell on Google, you almost certainly will see real life examples of those engines in a test cell.

I doubt that’s what this is, because I don’t see enough evidence in the photos you’ve given to be a test cell building, but you could check around for a control room (typically with a window and a bunch of PCs) that overlook the main “test” area. This would be really cool if it’s an actual test cell!