This position is a verification of the build process of the airplane. It tests the systems and verifies that they are operating per design. This is the beginning of verifying things such as not leaks in the hydraulic or coolant systems. Initial rigging of flight controls, and testing of systems like the landing gear. Without these systems being tested and moving through the process Boeing has said they will follow to prove the aircraft is built as designed the aircraft would not receive its airworthiness from the FAA or other governing bodies around the world.