Include a file in a plugin

[xXZarghamXx]

At some point one of my plugin , i need to include a file , how do i do that ?

The file name is test.php and it contain a simple hello world.The file is found in the forums directory in a folder called devfolder
<?php echo "Hello World"; ?>

In a real example , the file that i will include will contain code to update some entries in a database so there is nothing to show in the template