<?php
ob_start();
echo "*** Testing session_decode() : error functionality ***\n";
$data = "foo|a:3:{i:0;i:1;i:1;i:2;i:2;i:3;}guff|R:1;blah|R:1;";
for($index = 0; $index < strlen($data); $index++) {
    if(session_status() != PHP_SESSION_ACTIVE) { session_start(); }
    echo "\n-- Iteration $index --\n";
    $encoded = substr($data, 0, $index);
    var_dump(session_decode($encoded));
    var_dump($_SESSION);
};

$file_c = __DIR__ . "file_does_not_exist1";
$file_p = __DIR__ . "file_does_not_exist2";
file_put_contents($file_c, "<?php require '$file_p'; class c extends p {} ?>");
file_put_contents($file_p, '<?php class p { protected $var = ""; } ?>');
require $file_c;
$a = new c();
require $file_c;
?>