/usr/share/javascript/mathjax/test/ is in libjs-mathjax 2.4-2.
This file is owned by root:root, with mode 0o755.
..
/usr/share/javascript/mathjax/test/examples.html
/usr/share/javascript/mathjax/test/index-images.html
/usr/share/javascript/mathjax/test/index.html
/usr/share/javascript/mathjax/test/localization.html
/usr/share/javascript/mathjax/test/sample-all-at-once.html
/usr/share/javascript/mathjax/test/sample-asciimath.html
/usr/share/javascript/mathjax/test/sample-autoload.html
/usr/share/javascript/mathjax/test/sample-dynamic-2.html
/usr/share/javascript/mathjax/test/sample-dynamic-steps.html
/usr/share/javascript/mathjax/test/sample-dynamic.html
/usr/share/javascript/mathjax/test/sample-eqnum.html
/usr/share/javascript/mathjax/test/sample-eqrefs.html
/usr/share/javascript/mathjax/test/sample-loader-config.html
/usr/share/javascript/mathjax/test/sample-loader.html
/usr/share/javascript/mathjax/test/sample-macros.html
/usr/share/javascript/mathjax/test/sample-mml.html
/usr/share/javascript/mathjax/test/sample-signals.html
/usr/share/javascript/mathjax/test/sample-tex.html
/usr/share/javascript/mathjax/test/sample.html