CreditCardService.java

package com.example.unit.testing.domain;

import ...;

@Service
public interface CreditCardService {
	boolean isMaxedOut(String creditCardNumber, Double amount);

	LocalDate expirationDate(String creditCardNumber);
}

CreditCardWebservice.java

package com.example.unit.testing.infrastructure;

import ...;

/**
 * Implementation of the creditCardService that calls the webservice of the bank (for example).
 * In the real world, this would contain HTTP calls, Soap, rest...
 */
@Service
public class CreditCardWebservice implements CreditCardService{

	@Override
	public boolean isMaxedOut(String creditCardNumber, Double amount) {
		return false; 
	}

	@Override
	public LocalDate expirationDate(String creditCardNumber) {
		return LocalDate.of(2018, 01, 01);
	}
}

Customer.java

package com.example.unit.testing.domain;

import ...;

@Entity
public class Customer {

	@Id
	private Long tid;
	
	private List<Order> orders = new ArrayList<>();
	
	public Long getTid() {
		return tid;
	}
	
	public Order placeOrder(Long itemId) {
		Order o = new Order(this, itemId);
		this.orders.add(o);
		return o;
	}

	/** Return orders that are not failed or closed */
	public List<Order> getProcessingOrders() {
		return orders.stream()
				.filter(o -> o.getStatus().equals("IN PROGRESS") || o.getStatus().equals("NEW"))
				.collect(Collectors.toList());
	}

}

Order.java

package com.example.unit.testing.domain;

import...;

@Entity
public class Order {

	@Id
	private Long tid ;
	
	private String status;
	
	private Customer customer;
	
	private Long item;
	
	public Order(Customer customer, Long itemId) {
		this.customer = customer;
		this.item = itemId;
		this.status = "NEW";
	}

	public Double calculateAmount() {
		return (item.hashCode() % 1000) / 100.0;
	}
	
	public void processPayment(boolean paymentSuccess) {
		this.status = (paymentSuccess) ? "IN PROGRESS" : "PAYMENT FAILED";
	}
	
	public Long getTid() {
		return tid;
	}

	public String getStatus() {
		return status;
	}

	public Customer getCustomer() {
		return customer;
	}
	
}

OrderApplication.java

package com.example.unit.testing.application;

import ...;

@Service
public class OrderApplication {
	@Autowired
	CustomerRepository customerRepository;
	
	@Autowired 
	OrderRepository orderRepository;
	
	@Autowired
	PaymentValidationService paymentValidationService;
	
	
	@Transactional
	public Long placeOrder(Long itemId, Long customerId, String creditCardNumber) {
		
		Customer customer = customerRepository.findOne(customerId);
		Order newOrder = customer.placeOrder(itemId);
		
		boolean paymentSuccess = paymentValidationService.verifyCreditCardPayment(creditCardNumber, newOrder.calculateAmount());
		newOrder.processPayment(paymentSuccess);
		
		orderRepository.save(newOrder);
		customerRepository.save(customer);
		
		return newOrder.getTid();
	}
	
	public String getOrderStatus(Long orderId) {	
		Order order = orderRepository.findOne(orderId);
		return order.getStatus();	
	}

	public List<Order> findOrdersForCustomer(Long tid) {
		
		return customerRepository.findOne(tid).getProcessingOrders();
	}
}

PaymentValidationService.java

package com.example.unit.testing.domain;

import ...;

@Service
public class PaymentValidationService {

	@Autowired
	CreditCardService creditCardService;
	
	public boolean verifyCreditCardPayment(String creditCardNumber, Double amount) {
		return !creditCardService.isMaxedOut(creditCardNumber, amount) 
				&& creditCardService.expirationDate(creditCardNumber).compareTo(LocalDate.now().plusMonths(3)) > 0 ;
	}

}