On November 30th, 2016, Mozilla shut down the persona.org services. Persona.org and related domains will soon be taken offline.
For more information, see this guide to migrating your site away from Persona:
https://wiki.mozilla.org/Identity/Persona_Shutdown_Guidelines_for_Reliers
If you're making a production system you will need to write integration tests that simulate logging a user in and out of your site using Persona.
If you're using Selenium for testing, consider using the bidpom library. The sites mockmyid.com and personatestuser.org may also be helpful.
You may also want to consider stubbyid.