BuyCdTest.java

class BuyCdTest {

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

	private int buy(int stock, double price, String creditCardNumber, Payments payments) {
		if(payments.process(price, creditCardNumber) == PaymentResponse.ACCEPTED)
			stock--;
		return stock;
	}	
}