Fatal Error Class not found - PHP Namespace

Hello I'm using the following php codes

<?php
namespace lab312\database;

class ScriptFactory

{


function __construct()
{

}

//outras funcionalidades


}

and

<?php
namespace  lab312\database\testes;
use lab312\database\ScriptFactory;

/* arquivo t.php*/
$script = new ScriptFactory();    

However when I call the Scriptfactory class it gives the following error:

Fatal error: Class 'lab312 \ database \ ScriptFactory' not found in t.php on line 17

Any tips?