CI Version 3.1.3 My Controller Call to undefined method

Hi,

I  am using CI Version 3.1.3

I have a created controller on application/core MY_Controller.php

<?php

class MY_Controller extends CI_Controller
{
    public function __construct()
    {
        parent::__construct();
    }
    
    public function test()
    {
        echo 'test';
    }
    
    
}


and try to call on application\controllers Dashboard.php

code is

<?php

    class dashboard extends CI_Controller {
        
        function __construct() {
        
        parent:: __construct();
        
        $this->load->model('admin_database');
        $this->load->helper('url');
        $this->load->library('session');
       

    }    
    
    public function index() {
       

        $this->test();
       
    }
    
    }


but its giving error 

A PHP Error was encountered
Severity: Error
Message: Call to undefined method dashboard::test()
Filename: controllers/Dashboard.php
Line Number: 22
Backtrace:


please some one help me, will thank full

thanks