Gist do post "Usando PHPUnit no Codeigniter via Hooks" Link: http://willmendesnetoprojects.wordpress.com/2013/02/24/usando-phpunit-no-codeigniter-via-hooks/

DisplayHook.php

<?php

class DisplayHook
{
    public function captureOutput()
    {
        $this->CI =& get_instance();
        $output = $this->CI->output->get_output();

        if (ENVIRONMENT != 'testing') {
            echo $output;
        }
    }
}