Test Driven Development: By Example

Chapter 15

Mixed Currencies

$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)

Now we are finally ready to add the test that started it all, $5 + 10 CHF:

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

This is what we’d like to write. Unfortunately, there are a host of compile errors. When we were generalizing from Money to Expression, we left a lot of loose ends laying around. I was worried about them, ...