how to connect database with codeigniter using mamp

I am trying to connect my database in code igniter in mamp server. here is my config file

$active_group = 'default';
$active_record = TRUE;

$db['default']['hostname'] = 'localhost:3306';
$db['default']['username'] = 'root';
$db['default']['password'] = '';
$db['default']['database'] = 'lalcoresidency';
$db['default']['dbdriver'] = 'mysqli';
$db['default']['dbprefix'] = '';
$db['default']['pconnect'] = TRUE;
$db['default']['db_debug'] = TRUE;
$db['default']['cache_on'] = FALSE;
$db['default']['cachedir'] = '';
$db['default']['char_set'] = 'utf8';
$db['default']['dbcollat'] = 'utf8_general_ci';
$db['default']['swap_pre'] = '';
$db['default']['autoinit'] = TRUE;
$db['default']['stricton'] = FALSE;

I put localhost:3306 because port number in mamp server for database is given 3306 .

here is my controller

class Testimonials extends CI_Controller{

    public function __construct() {
        parent::__construct();
        $this->load->library('database');
    }

    public function index(){
        $data=array();
        $this->load->model('testimonial_model');
        $this->load->database();
        $data['result']=$this->testimonial_model->get_testimonial();
        $this->load->view('testimonials_view',$data);
    }
}

here is my model

class Testimonial_model extends CI_Model{
    function get_testimonial(){
        $this->db->select('*');
        $this->db->from('testimonial');
        $this->db->order_by("r_id", "desc");

        $query=$this->db->get();
        return $result=$query->result();
    }
}

When i run this code then it showing the following error

A Database Error Occurred

Unable to connect to your database server using the provided settings.

Filename: C:\MAMP\htdocs\lalcoresidency\system\database\DB_driver.php

Line Number: 125

Please help me to find the solution