codeigniter - Why 404 Page Not Found error occurs except default controller

I am using OS Ubuntu.
I am creating the application on codeigniter and facing problem while I am running my code. Only default controller is working, other then that are not working and application through the error:

404 Page Not Found

The page you requested was not found.

Code: Controller Name: Test

defined('BASEPATH') OR exit('No direct script access allowed');

class Test extends CI_Controller {


    public function index()
    {
        echo "Hi this is Test Controller";
    }
}