Test-Driven Development with Python

Appendix E. Behaviour-Driven Development (BDD)

Now I haven’t used BDD “in anger,” so I can’t claim any sort of expertise, but I really like what I have seen of it, and I thought that you deserved at least a whirlwind tour. In this appendix, we’ll take some of the tests we wrote in a “normal” FT, and convert them to using BDD tools.

What is BDD?

BDD, strictly speaking, is a methodology rather than a toolset—it’s the approach of testing your application by testing the behaviour that we expect it to display to a user (the Wikipedia entry has quite a good overview). So, in some ways, the selenium-based FTs that I’ve shown in the rest of the book could be called BDD.

But the term has become closely associated with a particular set of tools for doing BDD, most importantly the Gherkin syntax, which is a human-readable DSL for writing functional (or acceptance) tests. Gherkin originally came out of the Ruby world, where it’s associated with a test runner called Cucumber.

In the Python world, we have a couple of equivalent test running tools, Lettuce and Behave. Of these, only Behave was compatible with Python 3 at the time of writing, so that’s what we’ll use. We’ll also use a plugin called behave-django.

Getting the Code for These Examples

I’m going to use the example from Chapter 18. We have a basic to-do lists site, and we want to add a new feature: logged-in users should be able to view the lists they’ve authored in one place. Up until this point, all lists are effectively anonymous. ...