Test Driven Development: By Example

Chapter 16

Abstraction, Finally

$5 + 10 CHF = $10 if rate is 2:1

$5 + $5 = $10

Return Money from $5 + $5

Bank.reduce(Money)

Reduce Money with conversion

Reduce(Bank, String)

Sum.plus

Expression.times

We need to implement Sum.plus() to finish Expression.plus, and then we need Expression.times(), and then we’re finished with the whole example. Here’s the test for Sum.plus():

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public void testSumPlusMoney() {
   Expression fiveBucks= Money.dollar(5);
   Expression tenFrancs= Money.franc(10);
   Bank bank= new Bank();
   bank.addRate("CHF", "USD", 2);
   Expression sum= new Sum(fiveBucks, tenFrancs).plus(fiveBucks);
   Money result= bank.reduce(sum, "USD");
   assertEquals(Money.dollar(15), result);
}

We could have created a Sum by adding ...