September 22, 2007

Turning a corner on unit testing

Posted in Coding, Development, Me at 3:53 pm by mj

I think I’ve finally done it.

This week, I found myself struggling within the confines of existing infrastructure code that had no unit tests. The task was relatively simple: a new feature at the infrastructure-level that would enable many other product-level features in coming months. If I’d gone down the hackish route and not worked at the infrastructure level, I could’ve isolated this code and tested it in complete isolation. But that would just lead to more bugs down the road, and I’d still have a lot of integration testing to do.

It was one of the more painful and slow development experiences in recent memory. Even worse than dealing with 10-year old, undocumented, legacy Perl code written by non-programmers. Yeah, that painful.

For a long time, I contended that unit testing’s primary benefit was long-term: ensuring that refactoring code which you did not write and do not fully understand does not break. And that you need to reach a certain critical mass in terms of number and variety of tasks before it becomes effective. And that’s still true. I think my skepticism rubbed off, too, because I hardly hear anyone saying, “But the unit tests pass, there can’t be a bug” anymore.

But then I started looking at how I approached the practice of programming. Before I write code–often as part of designing the system–I write out stubs of how I’m going to use the code. Because an aesthetically unpleasing or overly complicated API is an error-prone API. And it dawned on me that this is one of the big benefits of test-first development.

Last year, when I read Agile Software Development: Principles, Patterns, and Practices (finally after it had been on my bookshelf for years), it was a bit like a revelation. Agile development, really, is formalizing what are otherwise good development-time practices anyway. So I resolved to better formalize my development activities.

It’s taken a while, but now I am so accustomed to using unit tests to isolate problems, and the quick turnaround that entails, that there is a significant mental barrier to any other way of doing it. I’ve turned that corner and am heading down NotReallyUtopiaButGoodEnough Street.

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