Generating a single unit test for a function inside of a controller Symfony2/PHP

I have a function that exists within a controller. I want to that the logic is sound by writing a small unit test with assertions to match correctly with the output of the function.

I've created a new unit folder to house all the little unit tests for the controller. The correct term may be a functional test?

This is the current set up I have to house all of the assertions for the function. My question is, out of all the functions that exist in this external controller, how can I bring that function in and perform a test on the logic within it?

<?php


namespace Acme\SimplewanBundle\Tests\Unit;

use Doctrine\ORM\Tools\SchemaTool;

class ConfigControllerUnitTest extends \PHPUnit_Framework_TestCase {


    public function testValidIpRange() {





    }

}