Insert

@Transactional
public OrderDTO insert(OrderDTO dto) {
	
	Order order = new Order();
	
	order.setMoment(Instant.now());
	order.setStatus(OrderStatus.WAITING_PAYMENT);
	
	User user = userService.authenticated();
	order.setClient(user);
	
	for (OrderItemDTO itemDto : dto.getItems()) {
		Product product = productRepository.getReferenceById(itemDto.getProductId());
		OrderItem item = new OrderItem(order, product, itemDto.getQuantity(), product.getPrice());
		order.getItems().add(item);
	}
	
	repository.save(order);
	orderItemRepository.saveAll(order.getItems());
	
	return new OrderDTO(order);
}

Mockaremos o UserService, o ProductRepository, OrderItemRepository e UserService com o @Mock, visto que tudo isso é usado no método acima.

Além disso, criar um existingProductId, nonExistingProductId e um Product utilizando a Factory.