如何使用codeigniter-predis库在redis中订阅？

I have to publish "testing" channel and listen into "mytesting()" but publish is successfully done. but on subscribe mytesting() not executed.

public function test()
{
    $this->redis_connection();

    $this->redis->publish('testing',"hi");

    try
    {
      $success=$this->redis->subscribe('testing','mytesting');
      print_r($success);

    }catch(Exception $e)
    {
      print_r($e->getMessage());
    }
}

public function mytesting($reds, $chan, $stdout)
{
    return $chan;
}

Try to use this library for subscribe in redis

CodeIgniter Redis : https://github.com/joelcox/codeigniter-redis