XPS Associates have released two testing products for XPS:
More information on the test suites from XPS Associates on XPS Review and c-xps.
In a related post  John Ingram has reviewed the Software Imaging XPS viewer and provided comparison rendering and performance details with the IE-host viewer in .Net and the Brava! viewer from informative graphics. I’d be interested to see how other implementations compare…
 you need to read the full post on the main XPS review page since the direct link has a truncated version (or at least when using IE8b2)