This site hosts the XProc (3.x) test suite along with several different browsable views of it.
The test suite repository is https://codeberg.org/XProc/test-suite.
View all of the tests:
Listed alphabetically.
Grouped by expected result.
Grouped by last revision date.
Grouped by element type.
Grouped by errors raised.
Grouped by required feature.
Combined with implementation reports.
Documentation for the test suite markup schema is also available.