Supplier/Util/SupplierUtil.php
static public function calculateReceivedQuantity(SupplierOrderItemInterface $item)
    {
        $quantity = 0;

        foreach ($item->getOrder()->getDeliveries() as $delivery) {
            foreach ($delivery->getItems() as $deliveryItem) {
                if ($item === $deliveryItem->getOrderItem()) {
                    $quantity += $deliveryItem->getQuantity();
                    continue 2;
                }
            }
        }

        return $quantity;
    }
static public function calculateReceivedQuantity(SupplierOrderItemInterface $item)
    {
        $quantity = 0;

        foreach ($item->getOrder()->getDeliveries() as $delivery) {
            foreach ($delivery->getItems() as $deliveryItem) {
                if ($item === $deliveryItem->getOrderItem()) {
                    $quantity += $deliveryItem->getQuantity();
                    continue 2;
                }
            }
        }

        return $quantity;
    }
Calculate the given supplier order item's received quantity.

@param SupplierOrderItemInterface $item

@return float