Codecetion Stub测试静态方法

我有类：

class Subscribe
{
    public static function isSubscribe($email)
    {
        return true;
    }
}

我的测试：

    public static  function testIsSubscribe()
{
    $subscribe = new 'Model'Subscribe();
    $object = Stub::make($subscribe, ['isSubscribe' => 'isSubscribe']);
    $this->assertEquals('isSubscribe', $object->isSubscribe(['email' => 'email@gmail.com']));
}

但是，测试静态类testIsSubscribe()给了我异常

PHPUnit_Framework_MockObject_BadMethodCallException：