$ sudo apt-get update
$ sudo apt-get install phpunit-mock-object 

phpunit-mock-object is installed in your system.

Make ensure the phpunit-mock-object package were installed using the commands given below,

$ sudo dpkg-query -l | grep phpunit-mock-object *

You will get with phpunit-mock-object package name, version, architecture and description in a table

phpunit-mock-object package basic information: