unserialize callback

gistfile1.php

<?php

function unserialize_callback($className) {
    if (! class_exists($className)) {
        throw new RuntimeException('class not found: ' . $className);
    } else {
        throw new RuntimeException('deserialization of ' . $className . ' failed');
    }
}

ini_set('unserialize_callback_func', 'unserialize_callback');

try {
    $o = unserialize('O:4:"Test":0:{}');
}
catch (\Exception $e) {
    echo $e->getMessage();
}