Supplier/EventListener/SupplierOrderListener.php
protected function updateState(SupplierOrderInterface $order)
    {
        $changed = $this->stateResolver->resolve($order);

        // If order state is 'completed' and 'competed at' date is not set
        if ($order->getState() === SupplierOrderStates::STATE_COMPLETED
            && null === $order->getCompletedAt()
        ) {
            // Set the 'completed at' date
            $order->setCompletedAt(new \DateTime());
            $changed = true;
        }

        return $changed;
    }
protected function updateState(SupplierOrderInterface $order)
    {
        $changed = $this->stateResolver->resolve($order);

        // If order state is 'completed' and 'competed at' date is not set
        if ($order->getState() === SupplierOrderStates::STATE_COMPLETED
            && null === $order->getCompletedAt()
        ) {
            // Set the 'completed at' date
            $order->setCompletedAt(new \DateTime());
            $changed = true;
        }

        return $changed;
    }
Updates the state.

@param SupplierOrderInterface $order

@return bool Whether or not the supplier order has been changed.