I've got a hard drive that you could copy
Almost 22 days of non-stop listening should keep you occupied
Nah, just kidding. I'd say good test tracks on such an event are tracks that both have excellent recording/mastering and people are likely to know so they have a mental image to compare the headphone against.
The recent re-issue of
Led Zeppelin - Kashmir should tick both boxes and would be my primary choice
If you want a list of songs (mix of genres, one per letter in the alphabet to restrain myself):
AC/DC - Whole Lotta Rosie
Bach (preferably the version by Gardener)- Matthäus-Passion, opening choir
Caribou - All I Ever Need (less know but bloody amazing and good to test bass)
Daft Punk - Give Life Back to Music
Explosions in the Sky - Your Hand in Mine (it's hard to find well known post-rock)
Florence and the Machine - Dog Days Are Over
Gorillaz - Clint Eastwood
Hundred Waters - Murmurs (not well known, but one of my favourite test tracks)
Iron Maiden - The Trooper (preferably the version from 'Live in Donington')
Johnny Cash - Hurt
Kanye West - Black Skinhead
Louis Armstrong - Hello, Dolly
Metellica - Enter Sandman (S&M live version)
Nightwish - Nemo
Of Monsters and Men - Little Talks
Pendulum - Watercolour (or witchcraft if you don't mind the intro)
Queen - Bohemien Rapsody
Radiohead - Everything in Its Right Place
Simon and Garfunkel - The Sound of Silence
Tom Odell - Another Love
Used, The - The Bird and the Worm
Volcano Choir - Seven Nation Army
Wardruna - Helvegen (or, if you're not into pagan music: White Lies - E.S.T. )
Xzibit - Papparazi (also the only artist I have that starts with an x
)
Yeah Yeah Yeahs - Skeleton
Ziggy Marley - Love is my Religion