What is the One Test Track That Tells You Almost Everything About A System?

Good suggestions for test tracks but: 

You may need several to truly assess your system  

You also need a good recording of a symphony orchestra and not just these studio bound somewhat manipulated recordings. 
If you can cleanly, transparently and dynamically reproduce the second movement of the Shostakovich Symphony #10-Second Movement recorded on DG with the Boston Symphony conducted by Nelsons in a live HiRes recording then you have an excellent system. Even if you don’t like classical music just spend 4+ minutes listening to this track. It’s a true test of the ability of your system to handle everything and also deliver a life-like you are there experience. Warning: It will expose every weakness 

You should hear a wide soundstage with depth. Great imaging, large dynamic swings, deep low end, clean instrument separation and silky airy strings extending beyond the left speakers. 

"From a Standstill" - Bella Sonus (Enamoured LP)

From the start, this well-layered track displays a wide frequency spectrum and well-delineated spatial elements that challenge both soundstage width and depth rendering, as well as expose a system’s ability to reproduce deep sub-bass transients with clarity and control. 

"Nature Boy" - Art Pepper (Essential Standards)

A more "organic" test of timbral accuracy and soundstage layering.

"Ruiner" - Nine Inch Nails (The Downward Spiral)

A test of a sytem’s ability to separate complex layers - plenty of phasing tricks that challenge soundstage width and depth rendering capabilities and room acoustics.

@pinwa I noticed The Astounding Eyes of Rita in your Playlist. I love this album!  I use the track "Waking State" in one of my demo playlists. 

'Fix it 'on Black acid soul By Lady Blackbird 

'Try to sleep' on duets special by Chrissy Hyde.

Two great vocal tracks to evaluate on a system.

I wasn't familiar with "Nardis", so I just gave it a listen.  Great track!  As a drummer, I enjoyed hearing the drum solo and the presentation of the percussion very much.  

I also agree with others that a good classical music track will tell a lot about a system's performance.  My personal favorite work for evaluating a system is Mahler's 2nd Symphony.  As an amateur choral singer, I have experienced this work on the stage, as well as many times from the audience, and I know it well.  The recording by Zubin Mehta and the Vienna Philharmonic is a personal favorite.  The ability of a system to convey the most silent sections as well as the monster finale will tell you a lot.