Wrong Hook Can Kill Hit Song: Garbage in, garbage out. When testing music, if the hook is wrong then the results may very well be wrong. One glaring example was Kellie Pickler's first single, "Red High Heels". The standard hook most used did not capture the unique part of the song, but instead focused on the title (as do most hooks). A hit song lost. Another example, "Red Dirt Road" a moderate hit for Brooks and Dunn. If you tested the correct hook (which most did not) you'd have found this song to be a strong power gold.
I also believe that the essence of some songs cannot be captured in a five to ten second hook. That doesn't mean they don't resonate with the audience. It just means they don't test well. Some of Keith Urban's best songs haven't tested as well as I believe they were actually accepted by the audience. The depth of some music goes beyond a hook.
Testing is a tool; one of several used to determine airplay. But it is not nor should it be the be all and end all in making music decisions. Knowing your audience, your market, sales, competitive strategy along with testing are all factors in making goods music decisions.