tensionload

The smiles suggest this test team met their goal or schedule deadline. Note the pocket protectors and that there are no smartphones. Hand-carried phones didn't exist, had poor coverage, or were expensive. In higher resolution photos, some of the team nametags may be readable.

After some head scratching, I believe this is probably a structural test for some kind of engine pylon. This would be a tough test to design because the pylon doesn't just support the static load of the engine hanging off the wing. It also must support tens-of-thousands of foot pounds of maximum forward trust and reverse thrust.

Tags are locked on this image also.

This looks like a tension load test on the pylon. Notice the hydraulic cylinders, a load cell above each one, a power supply and load cell readout in the foreground. Note the chalk marking for forward and tail on the girder at right. Please feel free to correct any bogus comments in the comments below.

Tags are locked out from editing on this image. I could be tagged "load cell", "structural test.," and "static load test". I see three load cells.