Update 2013-12-08-unit-test-your-symfony2-bundle-di-like-a-boss.markdown

Good article but  $configuration is not defined obviously is $resource

    protected function loadConfiguration(ContainerBuilder $container, $resource)
    {
        $loader = new XmlFileLoader($container, new FileLocator(__DIR__.'/Fixtures/Xml/'));
        $loader->load($configuration.'.xml');
    }