<?php
class Doukaku
{
    function Doukaku()
    {
    }

    function test_Doukaku()
    {
    }

    function hello()
    {
        print("hello world!");
    }

    function test_hello()
    {
    }
}

$doukaku = new Doukaku();
$result = array();
foreach (get_class_methods($doukaku) as $method) {
    if (strpos($method, "test_") === 0) {
        $result[] = $method;
    }
}

var_dump($result);
?>