Woocommerce: trying to change priority, add a custom tab and hide description tab if void

functions.php

add_filter( 'woocommerce_product_tabs', 'woo_new_product_tab' );
function woo_new_product_tab( $tabs ) {
	
global $post;

$tabs['description']['priority'] = 25;
$tabs['reviews']['priority'] = 55;
$tabs['test_tab'] = array(
	'title' 	=> __( 'test_tab', 'woocommerce' ),
	'priority' 	=> 50,
	'callback' 	=> 'woo_new_product_tab_content'
	);

$exists = get_post_meta($post->ID, 'product_description', true);
if ($exists == "") {
    unset($tabs['description']);
}
	return $tabs;

}
function woo_new_product_tab_content() {

	// The new tab content

	echo '<h2>New Product Tab</h2>';
	echo '<p>Here\'s your new product tab.</p>';
	
}

Is there someone that can help me in finding why I cannot get test_tab? All the rest works greatly.