/usr/share/man/man3/XTestDiscard.3.gz is in libxtst-dev 2:1.2.2-1+deb8u1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/man/man3/XTestQueryExtension.3.gz
/usr/share/man/man3/XTestQueryExtension.3.gz