Add a custom global product tab in WooCommerce

/**
 * @see http://docs.woothemes.com/document/editing-product-data-tabs/
 */
add_filter( 'woocommerce_product_tabs', 'woo_new_product_tab' );
function woo_new_product_tab( $tabs ) {
	
	// Adds the new tab
	
	$tabs['test_tab'] = array(
		'title' 	=> __( 'New Product Tab', 'woocommerce' ),
		'priority' 	=> 50,
		'callback' 	=> 'woo_new_product_tab_content'
	);

	return $tabs;

}
function woo_new_product_tab_content() {

	// The new tab content

	echo 'New Product Tab';
	echo 'Here's your new product tab.';
	
}