If it had not failed, it could have been used for other tests, couldn't it ?
Test articles are subject to "conformity inspections" prior to acceptance for test. It may be the case that a previously tested part is used for a subsequent test, though such reuse would be describe and agreed in the test plan, and the test article would have to be inspected to assure that it was "test worthy" which would equate to airworthy - no defects. Deviations can be allowed, where they would not affect the outcome of the test. It is not in the applicant's interest to test a defective test article, as the test could be a false fail.
Where the test is a flight test, obviously, we intend that the aircraft is returned at least reusable, if not still certifiable. Examples would include over speed or over weight testing in flight, where an inspection of the aircraft following test should verify that the aircraft remains airworthy. Manufacturer's test prototype aircraft are rarely released into service, often because they don't exactly represent the final approved design anyway.
There are times when I'll plan a test to demonstrate compliance to the requirement, then the requirement plus a factor of safety (which may deform and ruin the test article), and then following removal of the test load, a test to destruction, to see
how it failed, rather than at what load it failed.