XSpec is a unit test and behaviour-driven development (BDD) framework for XSLT, XQuery, and Schematron. It is based on the Spec framework of RSpec, which is a BDD framework for Ruby.
XSpec consists of a syntax for describing the behaviour of XSLT, XQuery, or Schematron code, and some code that enables you to test the code against those descriptions.
To get started, check out the installation instructions for MacOS/Linux and Windows and how to write your first XSpec test.