"Litmus test" songs

I know, I know, you can't evaluate a component, let alone a whole system based on a single piece of music, or even a half-dozen pieces. That said, are there any songs out there that you use as litmus tests when evaluating a purchase? Some song that you use when you say, "If this gear doesn't sound good with this song, then I don't care what else it does, it's going back"?

For me the Number 1 is "It's For You" by Pat Metheny Group.