GoodCode.java

public class OrderCreationController {
    private final OrderRepository orderRepository;
    private final ProductCatalog productCatalog;

    public OrderCreationController(OrderRepository orderRepository, ProductCatalog productCatalog) {
        this.orderRepository = orderRepository;
        this.productCatalog = productCatalog;
    }

    public Response post(List<Item> requests) {
        Order order = new Order();
        order.setStatus(OrderStatus.CREATED);
        order.setItems(new ArrayList<>());
        order.setCurrency("EUR");
        order.setTotal(0D);
        order.setTax(0D);

	    requests.forEach(r -> {
		    Product product = productCatalog.getById(r.getProductId());

		    if (product == null) {
			    throw new UnknownProductException();
		    } else {
			    final Double unitaryTax = (product.getPrice() / 100) * product.getCategory().getTaxPercentage();
			    final Double unitaryTaxedAmount = product.getPrice() + unitaryTax;
			    final Double taxedAmount = unitaryTaxedAmount * r.getQuantity();
			    final Double taxAmount = unitaryTax * r.getQuantity();

			    final Item item = new Item();
			    item.setProductId(r.getProductId());
			    item.setQuantity(r.getQuantity());
			    item.setTax(taxAmount);
			    item.setTaxedAmount(taxedAmount);
			    order.getItems().add(item);

			    order.setTotal(order.getTotal() + taxedAmount);
			    order.setTax(order.getTax() + taxAmount);
		    }
	    });
		orderRepository.save(order);

		return new Response(200);
    }
}


public class OrderCreationControllerTest {
    private TestOrderRepository orderRepository;
	private OrderCreationController controller;

    @BeforeEach
    public void setup() {
        Category food = new Category();
        food.setName("food");
        food.setTaxPercentage(10D);

        Product salad = new Product();
        salad.setId(1);
        salad.setName("salad");
        salad.setPrice(3.56D);
        salad.setCategory(food);

        Product tomato = new Product();
        tomato.setId(2);
        tomato.setName("tomato");
        tomato.setPrice(4.65D);
        tomato.setCategory(food);

	    ProductCatalog productCatalog = new InMemoryProductCatalog(List.of(salad, tomato));
        orderRepository = new TestOrderRepository();
        controller = new OrderCreationController(orderRepository, productCatalog);
    }

    @Test
    public void sellMultipleItems() {
        Item saladRequest = new Item();
        saladRequest.setProductId(1);
        saladRequest.setQuantity(2);

        Item tomatoRequest = new Item();
        tomatoRequest.setProductId(2);
        tomatoRequest.setQuantity(3);

        List<Item> requests = new ArrayList<>();
        requests.add(saladRequest);
        requests.add(tomatoRequest);

        controller.post(requests);

        final Order insertedOrder = orderRepository.getSavedOrder();
        assertThat(insertedOrder.getStatus()).isEqualTo(OrderStatus.CREATED);
        assertThat(insertedOrder.getCurrency()).isEqualTo("EUR");
        assertThat(insertedOrder.getItems()).hasSize(2);
        assertThat(insertedOrder.getItems().get(0).getProductId()).isEqualTo(1);
        assertThat(insertedOrder.getItems().get(0).getQuantity()).isEqualTo(2);
        assertThat(insertedOrder.getItems().get(1).getProductId()).isEqualTo(2);
        assertThat(insertedOrder.getItems().get(1).getQuantity()).isEqualTo(3);
    }

    @Test
    public void unknownProduct() {
        List<Item> requests = new ArrayList<>();
        Item unknownProductRequest = new Item();
        unknownProductRequest.setProductId(-1);
        requests.add(unknownProductRequest);

        assertThatThrownBy(() -> controller.post(requests)).isExactlyInstanceOf(UnknownProductException.class);
    }
}

Repository for the full workshop: https://github.com/renanreismartins/good-code/tree/main