public function validate_add_cart_item($passed, $product_id, $quantity, $variation_id = '', $variations = '')
 {
     if (WC_Extension_Boilerplate_Helpers::is_product_checkbox($product_id)) {
         wc_add_notice(__('This is a sample notice message', 'woocommerce-extension-boilerplate'), 'notice');
     }
     if (WC_Extension_Boilerplate_Helpers::get_sample_number($product_id) < 10) {
         $passed = false;
         wc_add_notice(__('This is a sample error message', 'woocommerce-extension-boilerplate'), 'error');
     }
     return $passed;
 }