CodeIgniter : Routing URL on Codeigniter
You are being redirected because $this->uri->segment(3) is not returning anything as your URL http://localhost/norwin/group/'group_name' have only 2 segments.
Codeigniter $this->uri->segment(n); works in the following way.
it will return
$this->uri->segment(1); // group$this->uri->segment(2); // group_name$this->uri->segment(3); // some_testyou have to change $this->uri->segment(3) to $this->uri->segment(2)