This article is part 4 in a series in which I’m doing a well-known code kata in the “TDD as if you meant it” style. I’m also strictly following the 4 rules of simple design and looking for opportunities to use implicit coupling to drive refactoring under the Once And Only Once rule. (If you missed the start of this series you can catch up with part 1 here.)

This is looking like being a long series of articles, so make sure you subscribe (it’s free!) so you don’t miss anything.

Last time I spent qu...