In March 2009 we started autotooling it, removing cruft, general weirdness and over time it became more useful. Many thanks here to Dan Nicholson, Aaron Plattner and Jon Turney. Now we've finally moved it from various $HOME directories to a git repo proper. The work is not completed yet though. The code does show its age and many a cleanup work is needed to drag XTS into the future. Kicking and screaming may be involved, swearing will definitely be part of that process.
To get the test suite, run
git clone git://anongit.freedesktop.org/git/xorg/test/xts.git
It is now at a stage where it pretty much runs with the usual autoreconf/configure/make steps and spits out results. The usefulness of those results is in debate, they all need auditing. You must run it against a plain X server, running a window manager will alter the results.
Note that XTS is a developer tool, be aware that it's inner workings and output may be confusing. If you look at it long enough, you may see the matrix.