Test Driven Development: By Example

Chapter 13

Make It

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

$5 + $5 = $10

We can’t mark our test for $5 + $5 done until we’ve removed all of the duplication. We don’t have code duplication, but we do have data duplication—the $10 in the fake implementation:

Bank

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Money reduce(Expression source, String to) {
   return Money.dollar(10);
}

is really the same as the $5 + $5 in the test:

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public void testSimpleAddition() {
   Money five= Money.dollar(5);
   Expression sum= five.plus(five);
   Bank bank= new Bank();
   Money reduced= bank.reduce(sum, "USD");
   assertEquals(Money.dollar(10), reduced);
}

Before when we’ve had a fake implementation, it has been obvious how to work backward to the real implementation. ...