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