When trying to install the Psysh Bundle from Theo Fidry in a Symfony 2.3 project, I ran into a bug. Since Theo Fidry only seems to maintain a newer version of the bundle (he only has a master branch), I decided to fork.

composer require --dev ameenross/psysh-bundle

Then, enable the bundle by updating your app/AppKernel.php file to enable the bundle:

<?php
// app/AppKernel.php

public function registerBundles()
{
    //...

    if (in_array($this->getEnvironment(), ['dev', 'test'])) {
        //...
        $bundles[] = new Fidry\PsyshBundle\PsyshBundle();
    }

    return $bundles;
}