--TEST--
Bad unserialize_callback_func
--FILE--
<?php
ini_set('unserialize_callback_func','Nonexistent');
$o = unserialize('O:3:"FOO":0:{}');
var_dump($o);
echo "Done";
?>
--EXPECTF--
Warning: unserialize(): defined (Nonexistent) but not found in %s on line %d
object(__PHP_Incomplete_Class)#%d (1) {
  ["__PHP_Incomplete_Class_Name"]=>
  string(3) "FOO"
}
Done