PHP OOP Gracefull __autoload失败

Question

Say I have the following:

function __autoload($class) { 
    if(file_exists("{$_SERVER['DOCUMENT_ROOT']}/etc/".strtolower($class).".php")) { 
        require_once strtolower($class).".php"; 
        return true;
    } else {echo "failed";}
} 

class test {
    public function __construct() {
        $this->db = new Database();
        $this->auth = new Authentications();
    }
}

$t = new test();

The file authentications.php does not exist. However I want to be able to handle that gracefully, at the moment I get the following output:

failed Fatal error: Class 'Authentications' not found in core.php on line 15

How can I handle this gracefully? I want to be able to output my own error or carry on - whichever I choose.