$ sudo apt-get update
$ sudo apt-get install libxtst6-udeb 

libxtst6-udeb is installed in your system.

Make ensure the libxtst6-udeb package were installed using the commands given below,

$ sudo dpkg-query -l | grep libxtst6-udeb *

You will get with libxtst6-udeb package name, version, architecture and description in a table

libxtst6-udeb package basic information: