Error when using PDO - php

Question

So I just finally installed the PDO drivers, and now I have another issue. When I try to use
<?php
$username = "root";
$password = "allen123";
$conn = new PDO('mysql:host=localhost;dbname=test', $username, $password);
?>
Just to connect to the DB, I get the following error
Fatal error: Uncaught exception 'PDOException' with message
'SQLSTATE[HY000] [2002] No such file or directory' in
/Users/idrisk/Colourity/site/index.php:4 Stack trace: #0
/Users/idrisk/Colourity/site/index.php(4):
PDO->__construct('mysql:host=loca...', 'root', 'allen123') #1 {main}
thrown in /Users/idrisk/Colourity/site/index.php on line 4
I've looked at other posts on SO about this issue, but they all seem different. Any ideas?
EDIT
So I installed the drivers via Macports and this is what I get once It was installed
To use mysqlnd with a local MySQL server, edit /opt/local/etc/php55/php.ini and set mysql.default_socket, mysqli.default_socket and pdo_mysql.default_socket to the path
to your MySQL server's socket file.
For mysql51, use /opt/local/var/run/mysql51/mysqld.sock
For mysql55, use /opt/local/var/run/mysql55/mysqld.sock
For mysql56, use /opt/local/var/run/mysql56/mysqld.sock
For mariadb, use /opt/local/var/run/mariadb/mysqld.sock
For percona, use /opt/local/var/run/percona/mysqld.sock`
The other answers say to use something else.