$ sudo apt-get update
$ sudo apt-get install elpa-ert-async 

elpa-ert-async is installed in your system.

Make ensure the elpa-ert-async package were installed using the commands given below,

$ sudo dpkg-query -l | grep elpa-ert-async *

You will get with elpa-ert-async package name, version, architecture and description in a table

elpa-ert-async package basic information: