WooCommerce - Add new product tab

functions.php

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>';
	
}

Another Useful Example:

class Woo_Product_Tabs{

	public static function init() {
		add_action( 'woocommerce_product_write_panel_tabs',array( 'Woo_Product_Tabs', 'add_product_delivery_panel_tab' ) );
		add_action( 'woocommerce_product_data_panels',array( 'Woo_Product_Tabs', 'add_product_delivery_panel_data' ) );
	}


	public static function add_product_delivery_panel_tab() {
		?>
        <li class="delivery_options delivery_tab">
            <a href="#delivery_product_data"><?php echo esc_html__( 'Delivery', 'theme_name' ); ?></a>
        </li>
		<?php
	}

	public static function add_product_delivery_panel_data() {
		global $post;
		?>
        <div id="delivery_product_data" class="panel woocommerce_options_panel">
            <div class="options_group">
				<?php
				$info = get_post_meta( $post->ID, 'info', true );
				wp_editor( htmlspecialchars_decode( $info ), 'info', array() );
				?>
            </div>
        </div>
		<?php
	}

}

Woo_Product_Tabs::init();