mailgun-php/vendor/phpunit/phpunit-mock-objects/Tests/_files/MethodCallbackByReference.php

<?php
class MethodCallbackByReference
{
    public function bar($a, &$b, $c) {
        Legacy::bar($a, $b, $c);
    }

    public function callback($a, &$b, $c) {
        $b = 1;
    }
}