Recently the "prefer-lowest" option of Composer was mentioned in relation to testing for Symfony-based applications. In this new post to his site Matthieu Napoli shows how you can do it on any project that uses the Travis-CI continuous integration service.

Composer just got a new awesome addition thanks to Nicolas Grekas: prefer the lowest versions of your dependencies. [...] This amazing option will install the lowest versions possible for all your dependencies. What for? Tests of course!

He includes all the instructions you'll need to get your Travis build using this command line option, starting with testing it on your own system first. He shows a basic ".travis.yml" file with the configuration you'll need to provide it use the "prefer-lowest" (check out line 17). He does point out that you'll need to run a "composer self-update" first though, as Travis hasn't quite caught up with the latest Composer that includes this option.