Jeni Tennison has announced an utility for unit-testing XSLT stylesheets:
I've just developed a set of stylesheets that are designed to support unit testing of XSLT stylesheets. You embed tests in the stylesheet and can run a script (or configure your editing environment) to extract and run them and create an HTML report on the result. Further details and the download is available from:XSLT 2.0 engine (Saxon 8.4B or later) is required.
http://www.jenitennison.com/xslt/utilities/unit-testing/
Also she announced that her long-awaited "Beginning XSLT 2.0: From Novice to Professional" book is finally out:
Highly recommended for XSLT beginners.
There is also another unit testing frame work for XSLT (UTF-X). It lacks in documentation, but is feature rich and quite mature and stable. We have been using it for 2 years.