Firstly, writing test-first permanently changed the way I write code .... They still tend to be short, descriptive and as self-contained as I can make them, and

Firstly, writing test-first permanently changed the way I write code .... They still tend to be short, descriptive and as self-contained as I can make them, and as a result easier to understand and change I learned exactly the same lessons from writing code in a functional style. The experience changed my style for the better, and that carries over even when I'm using a language that doesn't lend itself very well to functional programming.