<?php

/**
 * Add a custom tab to WooCommerce products
 *
 * @param (array) $tabs - Registered tabs
 * @return (array) $tabs - Updated array of tabs
 *
 * @author UltimateWoo <www.ultimatewoo.com>
 */
function uw_custom_product_tab( $tabs ) {

	global $post;

 	$tabs['uw_custom_product_tab'] = array(
	 	'title' => 'Test Tab',
	 	'priority' => 50,
	 	'callback' => function( $key, $tab ) {
	 		echo "Our custom test tab's content, added via PHP!";
	 	}
 	);

	return $tabs;
}
add_action( 'woocommerce_product_tabs', 'uw_custom_product_tab' );