Behavior Driven Development

I stumbled into this entirely by accident. As a follow-up to the Rails Tutorial project, I took a closer look at one corner of the sample app. The image upload feature of the sample app used a gem called carrierwave uploader to do most of the work. In the context of the tutorial, CarrierWave was a magic black box that was pulled in and used without much explanation. I wanted to better understand the features (and limitations) of CarrierWave for use (or not) in my own projects.
As is typical of open-source projects, the documentation that exists is relatively thin and occasionally backed by the disclaimer "for more details, see source code." I prefer better documentation up front but I thought: whatever, I'm a programmer, I can handle code spelunking. It should be a good exercise anyway.
Since I was exploring, I decided to poke my head into the first (alphabetically sorted) directory : /features/. And I was immediately puzzled by the files I read. The language is too formal to be conversational English for human beings, but too informal to be a programming language as I knew one. Some amount of Google-assisted research led me to the web site for Cucumber, the BDD tool used by the developers of CarrierWave.
That journey was fun, illuminating, and I haven't even learned anything about CarrierWave itself yet!