Testing and further discussions https://twitter.com/michaelmoussa/status/483937808122273792

World.php

<?php
namespace Hello;
class World
{
    public function display()
    {
        return imap_connect('imap.example.com');
    }
}

WorldTest.php

<?php
namespace Hello;
require __DIR__ . '/World.php';

class WorldTest extends \PHPUnit_Framework_Testcase
{
    public function testDisplay()
    {
        $world = new World();
        var_dump($world->display());
    }
}

function imap_connect($url) {
    return "Hello World";
}