In this recent post Sebastian Göttschkes shows how to use the vfsStream stream wrapper in a Symfony2 application to create tests that involve the local file system.

I read about vsfstream when skipping through the phpunit docs. Back then, I decided I don't need a virtual file system. Some time later, I had to test classes which read and write files and found myself creating and deleting temporary folders, messing around with nasty errors (like my favourite one where for some reasons tests fail when I don't use @runTestsInSeparateProcesses).

He walks you through the install process, how to register it in the Symfony2 autoloader (so you don't have to include the files each time) and how to include it (via namespace-based loading) in your tests.