[Loic]

I heavily recommend PHP farm to test your code with a given version of PHP: http://cweiske.de/tagebuch/Introducing%20phpfarm.htm

This allows you to have several versions of PHP, each one with a given php.ini, given list of extensions and a given PEAR.

[asm89]

If you have open-source projects on github, you should really checkout travis (http://travis-ci.org/). Travis is also able to run tests in different php environments and can be hooked into github to tests whenever you commit! :)