"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.
I often start with a well recorded voice. Sometimes I use the song "I know you by heart" off Eva Cassidy's 'Songbird' CD. If that does not paint a deeply holographic image, sound acoustic and incredibly detailed, and completely free of the speakers with some potential to stir the emotions, I usually stop there. If it works, I have around 20 diversified favourites on a range of albums to listen to.
I always include something that ONLY sounds good on a great system, crappy, if not painful, on mediocre setups...try Stan Kenton's West Side Story can be grueling or great!
I usually use trio jazz recordings im familiar with.Peter erskines recordings(palle danielson,john taylor).later are better.Bobo stensons war orphans is a great recording too.
Great question. I often use Ornette Coleman's "Ramblin'" to get the overall picture. Then I might go to a Schoenberg string quartet, like #4, to get the difficult space as a challenge. Then maybe all out baroque, like a Bach Orchestral suite. If I still like what I am hearing, I go to solo instrument pieces.
Last movement of Mahler's 6th by MTT and San Francisco. "The Drifter" on Justice Reocrd's "Strike a Deep Chord" and Odetta's "America" on the same record. "Poppa Was a Rolling Stone" on grp's "a twist of motown"; Jennifer Warnes' "If It Be Your Will" on "Famous Blue Raincoat"; "music for Organ, Brass and Timpani" on Sonoma. Karrin Allyson's "Blame it On My Youth" with Mike Metheny on flugel, I forget the album name.

I focus on different things on each. If it could be only one, it'd be the Mahler 6th because I haven't found a system that does that well that can't do all things well.

I always use these well recorded cuts:
. Diana Krall - A Case of You (Live in Paris)
. Rahsaan Roland Kirk - A Laugh for Rory (Inflated Tear)
. Art Pepper - Move (Art Pepper + 11)
. Terje Rypdal - Chaser (Chaser)
. Steve Hunter - The Idler (The Deacon)
. Otis Taylor - Resurrection Blues (White African)

And these not so well recorded cuts, but expect them to still sound good:
. Rory Block - Last Fair Deal Gone Down (Last Fair Deal)
. Paul Butterfield Blues Band - I Got a Mind to Give Up Living (East-West)

And this poorly recorded one which I only hope might not sound too awful:
. Reverend Horton Heat - Lie Detector (Holy Roller)
Paul Simon - Graceland - Boy in the Bubble, Graceland, Diamonds on the Soles of her Shoes

Steve Miller - Born 2b Blue - God Bless the Child

kd lang - Absolute Torch and Twang - Luck in My Eyes

Talking Heads - Naked - Nothing But Flowers
Talking Heads - Stop Making Sense - Burning Down the House, Life During Wartime

Miles Davis - Kind of Blue - So What (Columbia Mastersound) - only the bass in the beginning

Those will usually show up deficiencies pretty quickly. After those, I go to acoustic music, etc.
Another trick I use in testing out equipment is to try out flawed recordings. e.g. If you have a recording where you know that the guitar has a marginally harsh edge, then a great system doesnt correct this for you, or it will fail elsewhere.
Here are some albums I always take out.

Soundstage: Paul Kelly, "May 1992"
Electric guitar/decay,surge and whomp: Midnight Oil, "Earth and Sun and Moon"
Acoustic: James Taylor, "Fire and Rain"
Live Ambience: Neil Young,"On the Beach" and "Zuma".