wc-product-meta-3.php

<?php
/**
 * WC Meta Data ~ How to do this in WooCommerce 3 ?
 *
 * @link https://stackoverflow.com/questions/45540351/woocommerce-3-crud-how-to-do-this
 *
 * @link https://github.com/woocommerce/woocommerce/wiki/CRUD-Objects-in-3.0
 */
add_action( 'plugins_loaded', function() {
	if ( ! class_exists( 'WooCommerce' ) ) {
		return;
	}

	// Add tabs.
	add_filter( 'woocommerce_product_data_tabs', function( $tabs ) {
		$tabs['test'] = array(
			'label'    => 'TEST',
			'target'   => 'my_test_data',
			'class'    => array(),
			'priority' => 1,
		);
		return $tabs;
	} );

	// Add panels.
	add_action( 'woocommerce_product_data_panels', function() {
		?>
		<div id="my_test_data" class="panel woocommerce_options_panel">

			<?php woocommerce_wp_text_input( array(
				'id'                => '_my_test_data',
				'label'             => 'Test Input',
				'description'       => 'Lorem Ipsum',
				'value'             => get_post_meta( get_the_id(), '_my_test_data', true ),
				'placeholder'       => '',
				'type'              => 'text',
			) ); ?>

		</div>
		<?php
	} );

	// Save.
	add_action( 'woocommerce_process_product_meta', function( $post_id, $post ) {
		if ( isset( $_POST['_my_test_data'] ) ) {
			update_post_meta( $post_id, '_my_test_data', $_POST['_my_test_data'] );
		}
	}, 10, 2 );

} );