Test to see if save_post hook is firing

save-post-test.php

<?php
/**
 * Test to see if save_post is firing
 *
 * If it works, you should see an 'iso_save_post' entry in your wp_options table
 *
 */

function iso_test_save_post() {
	add_option( 'iso_save_post', 'is_saving!' );
}

add_action( 'save_post', 'iso_test_save_post' );