My thoughts would be to do the tests in stages so if any faults occur you can trace them and it makes fault finding simple. You should ideally have an inspection sheet in my mind that you fill in every time you run a test. each test should have numerical test requirments (eg revs, range, temperature, etc) and the tests must be repeatable. the inspection should be looking for things that can be proved not guess work (eg the plenum cracked not the plenum might have cracked). The test suites should be designed around the areas or situations that require investigation (temperature, revs, longevity, torsional stiffness in corners). Also realistically more than one plenum should be tested to ensure there are no manufacturing variances. The supplier should have the correct quality standards in place also.
I dont want to ramble too much but you get the idea. figure out what you want to investigate first, then design the test round this.