$ sudo apt-get update
$ sudo apt-get install posixtestsuite 

posixtestsuite is installed in your system.

Make ensure the posixtestsuite package were installed using the commands given below,

$ sudo dpkg-query -l | grep posixtestsuite *

You will get with posixtestsuite package name, version, architecture and description in a table

posixtestsuite package basic information: