BuyCdTest.java

	@Test
	void buyCdPaymentAccepted() {
		int stock = 10;
		double price = 9.99;		
		String creditCardNumber = "1234";		
		Payments payments = new PaymentsStub(PaymentResponse.ACCEPTED);		
		stock = buy(new CompactDisc(stock, price, payments), creditCardNumber);		
		assertEquals(9, stock );
	}

	private int buy(CompactDisc cd, String creditCardNumber) {
		int stock = cd.getStock();
		if(cd.getPayments().process(cd.getPrice(), creditCardNumber) == PaymentResponse.ACCEPTED)
			stock--;
		return stock;
	}