How to create mock for a method with reference parameters

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While testing PHP we need sometimes to create a mock for a method with reference parameters. I use returnCallback() from PHPUnit framework to to this. returnCallback() will call a function that imitates functionality of the original method. The original method can be either public or protected.

For example:

class A
{  
    function getReference(&$ref)
    {
        $ref = 99;
        return 0;
    }
}

class ATest extends PHPUnit_Framework_TestCase
{    
    function testgetReference()
    {
        $f = function(&$ref)
        {
            $ref = 100;
            return true;
        };

        $mock = $this->getMock('A');
        $mock->expects($this->any())
            ->method('getReference')
            ->will($this->returnCallback($f));

        $return = $mock->getReference($a);
        $this->assertEquals(100, $a);
        $this->assertTrue($return);
    }
}