It may be that actually fully stressing the parts is avoided, as it may risk weakening the part.
I've heard of various non destructive testing methods being used to check the integrity of metals in aerospace, such as ultrasound and radiography. This may well be enough if the part is actually made of what it's supposed to be.
+1 Make that part of the deal. We only need 2 items, but you will produce 4. We will then randomly pick 2 of them for testing, and then and only then if those 2 pass will we actually use the remaining 2 as needed.
This happens all the time in construction of multistory buildings. When the floors of concrete are poured, they also produce smaller sections of concrete from the same batches. As the concrete cures, it's strength is tested. This ensures that the concrete can support the weight designated in the plans. Better to watch a test pour fail than the building collapsing when cheap concrete fails under load.
[edit] oops, just read comments later in the thread stating the same thing
Maybe the reason they didn't is that doing so is expensive, should have already been done by the supplier, this was for an unmanned mission (which have significantly looser safety requirements), which was insured (I assume), and costs to some extent recoverable by lawsuits.
According to the DoJ article: "the replacement cost of frangible joints provided to the MDA that included SPI extrusions is approximately $15.3 million, and NASA incurred approximately $9 million in investigative and other costs to determine the impact of SPI extrusions on NASA operations."
For economic reasons, some compromise needs to be reached between assurance and insurance.
I've heard of various non destructive testing methods being used to check the integrity of metals in aerospace, such as ultrasound and radiography. This may well be enough if the part is actually made of what it's supposed to be.