Hi, Dozy.
I drive past
this every time I have to work up in the Everett plant - the fatigue test airframe that they encased in its large blue "exoskeleton" late last year. The rig is designed to push the plane through (hundreds of) thousands of taxi, takeoff, flight, landing, taxi cycles - and over a range of flight profiles.
The flight cycles include pressurization according to the "flight" profiles, so as well as the usual spider web of jacks/pulleys/weights, the rig incorporates the capability to pump up the fuselage.
Can't find the reference quickly here on a sunny Sunday, but there's a published number of flight cycles that had to be achieved before entry into service, and the fatigue airframe has to maintain a substantial "lead" over the highest in-service item.
EVERETT, Wash., Sept. 13 — Boeing has begun fatigue testing on the structural airframe of the 787 Dreamliner at the Everett, Wash., site. Fatigue testing involves placing the 787 test airframe into a test rig that simulates multiple lifecycles to test how the airplane responds over time.