Yes, but they did that on the ground, where the ratio of inside to outside pressure was much smaller than it would be at altitude, and the outside air density was much higher, so their tests are not necessarily representative of what would happen at high altitudes.
As I recall, they set up the best differential they could get - which was pretty close to the operational figure. The reactions of the fuselage in the initial second or so would have been under the same impetus, and thus almost identical. I thought it was a pretty good test, short of automating and airliner, and flying it to altitude!
