Hew Wolff


Variations in Test-Driven Development

london_traffic_lights“Red-Green-Refactor” is a familiar slogan from test-driven development (TDD), describing a popular approach to writing software. It’s been both popular and controversial since the 2000’s (see the recent heated discussions between David Hansson, Bob Martin, and others). I find that it’s useful but limiting. Here I’ll describe some interesting exceptions to the rule, which have expanded the way I think about tests.

The standard three-step cycle goes like this. After choosing a small improvement, which can be either a feature or a bug fix, you add a failing test which shows that the improvement is missing (“Red”); add production code to make the test pass (“Green”); and clean up the production code while making sure the tests still pass (“Refactor”). It’s a tight loop with minimal changes at each step, so you’re never far from code that runs and has good test coverage.

By the way, to simplify things, I’ll just say “tests” and be vague about whether they’re technically “unit tests”, “specs,” “integration tests,” or “functional tests”; the main thing is that they’re written in code and they run automatically.

Red-Green-Refactor is a very satisfying rhythm when it works. Starting from the test keeps the focus on adding value, and writing a test forces you to clarify where you want to go. Many people say it promotes clean design: it’s just easier to write tests when you have well-separated modules with reasonable interfaces between them. My personal favorite part, though, is not the Red but the Refactor: the support from tests allows you to clean things up with confidence, and worry less about regressions.

Now for the exceptions. Read more…


Function = Var + Return: A Functional Style of JavaScript Programming

Functional Programming with JavaScript isn't as hard as you think

Functional programming, for most working programmers, is exotic. I’ve been experimenting with it as a way to get cleaner code and to expand my mind a bit. Here I describe a minimal approach to JavaScript which makes it intensely functional.

Functional programming avoids side effects (also known as state or mutable data) by using functions that operate on other functions. It emphasizes expressions over commands, and computation over assignment. There are lots of functional languages, including Lisp (the original) and XSLT (the one I happen to know best).

JavaScript is a flexible language with first-class functions, so it supports a functional programming style. Usually people do this with a library such as Underscore.js, which provides array operations like “map” and “reduce” and function operations like “bind” and “compose”. This is very cool. For example, when you use “map”, you work at a higher level of abstraction. You don’t have to worry about a temporary index variable for iterating over the array, so the code becomes shorter and clearer.

Read more…