killer testing

test.php

<?php

class TestTest extends PHPUnit_Framework_TestCase
{
    public function testMock()
    {
        $user2 = $this->getMock('UserInterface');

        $user2->expects($this->any())
            ->method('getSalt')
            ->will(
                $this->returnCallback(function() use (&$user2) {
                    return $user2->getSalt();
                })
            );

        $user2->getSalt();
    }
}

interface UserInterface
{
    function getSalt();
}