I had my attention drawn to Google's XSpec toolkit
at this site.
This toolkit is describes as:
"XSpec consists of a syntax for describing the behaviour of your XSLT or XQuery code, and some code that enables you to
test your code against those descriptions."
and "a Behavior Driven Development framework for XSLT and XQuery"
To my untutored eye, this looks like a tool for "agile" development with XSLT - I would be interested in hearing from anybody who has used it.
Bill