How to append a customer to a newly created order?

Shopware 6 (English)
1

Based upon TestOrderpersister, this is how I create new orders:

            $order = new OrderEntity();
            $order->setUniqueIdentifier(md5($someUniqueData));

            $persister = new OrderPersister($this->orderRepository, $this->orderConverter);

            $token = Uuid::randomHex();
            $salesChannelContext = $this->salesChannelContextFactory->create($token, Defaults::SALES_CHANNEL);
            $persister->persist($cart, $salesChannelContext);

How can I inject the customer data (name, address…) into the order? It has a SetOrderCustomer method, but no SetCustomer() method. The aforementioned test file depends on injecting the customer data into the SaleschanenlContext, but it does so using a test-specific mock method.