Oh boy! XSpec v3.0 is scheduled for April this year, including (among other things) SchXslt 1.9.5 as replacement for the skeleton implementation. I'm at the ready to fix the issues that will be detected this way.

GitHub - xspec/xspec: XSpec is a unit test and behaviour-driven development (BDD) framework for XSLT, XQuery, Schematron, and (upcoming in v4.0) XProc.
XSpec is a unit test and behaviour-driven development (BDD) framework for XSLT, XQuery, Schematron, and (upcoming in v4.0) XProc. - xspec/xspec