Modern C++ Programming with Test-Driven Development

2.9 What If?

Our implementation assumes that the letter passed to ​encodedDigit​ will be found in the ​encodings​ map. We make the assumption to allow moving forward incrementally, writing only the minimal code needed to pass each test. But we still have the responsibility of thinking about code that may need to be written.

Will it ever be possible for ​encodedDigit​ to be passed a letter that doesn’t appear in the lookup map? If so, what should the function do? Wikipedia doesn’t answer the question. We could guess, but the better answer is to ask the customer. We don’t have one, but we can find a customer proxy online. A web search quickly turns up a handful of Soundex calculator apps. We enter ​A#​ into one of them and receive ​A000​ as a response. ...