The code for Chapter 12 of TDD by Beck is now on GitHub.
CH 12 - Addition, Finally In this chapter, we take a big test - which is addition cross-currencies, and reduce it to a simpler case of addition in a single currency. Wiht that - we have a metaphor - Expressions - which are currency independent - think of them like a wallet. Operations result in expressions - and if we think of the multiple ways that a currency combination in a wallet can have the same value - we introduce a "bank" as a way of converting to a single currency value at the end. This means - Expression will operation on Money. Then create a bank. Have the bank reduce the value to USD (for example)