wc-composable-product/tests/stubs/class-wc-order.php

<?php
/**
 * Minimal WC_Order stub for unit testing.
 */
class WC_Order extends WC_Data {
    protected $items = [];
    protected $order_notes = [];

    public function get_items($type = '') {
        return $this->items;
    }

    public function set_items($items) {
        $this->items = $items;
    }

    public function add_order_note($note) {
        $this->order_notes[] = $note;
    }

    public function get_order_notes() {
        return $this->order_notes;
    }
}