In Engineering there's an idea that if you can't eliminate a problem, you attempt to contain it and mitigate its effects.
That's exactly what they're trying to do with these tests on the External Tank of the Space Shuttle.
Basically the external tank carries a load of liquid hydrogen and oxygen required by the Space Shuttle during flight. It needs to be cooled so low that it creates ice build ups on the external tank. It's essentially a huge sophisticated pop can.
It's theorized that foam from the bipod ramp near the connection between the space shuttle and the external tank fell off during flight and struck the wing of the space shuttle causing damage to the tiles on the wing. This is based on sketchy coverage of Shuttle during launch showing foam striking the wing. What has always bothered me is that they can't really produce evidence that it was that piece of foam that caused the damage that lead to disaster. In reality it could have been anything. They base their findings on the launch STS-50 which showed considerable damage from a falling piece of foam. However it's still just a theory. NASA engineers have seen this happen on countless other launches. Some raised a red flag, but NASA in the end decided to ignore any potential damage. The truth is that many things besides foam can cause protective tiles to fall off during flight. Going nuts over coverage of some falling foam hitting the wing is the least of the Space Shuttle's many problems.
Engineers would usually call something like this a "design flaw." The only way to fix a design flaw is to scrap the design and start fresh.
Instead of scrapping the Shuttle they've chosen to try to mitigate the risk. Notice that they speak about inspecting the External Tank for "ice buildup." If Engineers were really convinced that the source of the problem was the bipod ramp foam they would test that component alone in a smaller test.
This large scale test I bet included an inspection of ice build ups in sensitive areas that NASA engineers decided on without any impetus by anyone else. Ice falling off the external tank and striking the wing are just as liable of a culprit, and my bet is that Engineers at NASA know it and that's why these intensive tests are being done.
It's convenient to point your finger at a piece of foam as the culprit because it makes everyone think you know what your talking about. The truth is that Engineering is sometimes filled with uncertainty, and it may be the worst thing to say but the truth is you really don't know.