Case study: Behaviour-driven development (BBD) using Behat and Drupal (Forest Desk)

J-P
Freelance developer at Magnetic Phield
Behat test running screenshot

Forest Desk is an intranet tool for curating syndicated news from many sources, to be re-syndicated to several public-facing websites

Longstanding clients of Agile Collective, the Global Canopy Programme (GCP) needed to retrieve news syndicated from many public sources, manage it via an internal application, then re-syndicate it reliably to several public-facing websites. This application - called Forest Desk -needed to be described and built “just in time”, both to fit the clear initial requirements but also to adapt to any discoveries made along the way.

Background

I was asked to work with Agile Collective to help GCP build Forest Desk, using our preferred framework of Drupal 7. It promised to be a neat, compact site, with the potential for good in-house user experience and great performance. However, while the fundamental goals of the project were clear, we all agreed that we needed to be able to:

  • support rapid iteration of features and just-in-time specification of the details,

  • while also being reassured that ongoing development was stable and correct.

With those two demands in mind, we decided very early on to work according to the paradigm of behaviour-driven development or BDD. Like test-driven development more generally, BDD improves understanding of, and adherence to, requirements. This is done via a 3-step process for each requirement:

  1. Formalise the requirements. In this case, we wrote them down as a semi-human-readable set of “scenarios” using a limited subset of English, called Gherkin.

  2. Use software to turn these scenarios into automated tests, and run them even before the required functionality is in place, to show they “fail as expected” in its absence.

  3. Build the required functionality (tweaking the scenarios where they were initially unclear) until the test passes.

This simple BDD process could be followed for each piece of functionality in turn, and embedded in a wider project-management framework like Scrum. Such an environment can lead to not just a usable end product, but also tried and tested functionality underpinning it, both now and the future.

Getting agreement

Everyone brings their own assumptions to a project. Very often two people can be using the same words and phrases to describe quite different ideas that each has in mind. The traditional approach for sounding out such potentially dangerous scope misalignment has been to do a lot of up-front discovery, but this can introduce delay and sometimes can even provide a false sense of security by becoming out of date, or by being so large that it hides inconsistencies which only become apparent as the deadline approaches.

Consequently on this project, we sounded out each requirement 'just in time'. That involves speccing it out only when required, and in terms of the behaviours of the website as the user tries to attain certain goals. Gherkin, the widely-supported syntax we use, imagines this behaviour from the site user’s perspective in a series of scenarios such as:

  • Given I am logged in

    • And I am on the homepage

  • When I click on “My account”

    • And I click on “Edit profile”

  • Then I should see a “Your username” element

    • And I should see a “Your password” element

Although bits of the above can be omitted, there’s not much deviation permitted from the format. And because it’s so restrictive, it requires people to spell out their thoughts more clearly, eliminating misunderstandings.

Still following the principle of just-in-time specification, we allowed ourselves to proceed even if we haven’t completely fleshed out the functionality, keeping subtle, hard-to-translate bits of functionality un(der)described at the specification stage; for example:

  • Given I am logged in

    • And I press a button and some custom functionality happens

  • Then I should see new content retrieved from some remote syndication

The italicised bits of the specification are not commonly understood by programs which can read Gherkin. But the point is that such a test will fail, and draw attention to itself rather than permit them to be forgotten. In the meantime, doing this allows us to keep moving, accepting as a team that either we needed to flesh such scenarios out further, or leave such sections to the developer’s judgment as an implementation detail.

How to get computers to understand the requirements

Next up: test whether the functionality has been correctly built using a separate application called Behat.

Behat can act just like a human being sat in front of a web browser (with some limitations), but can also utilise the rest of a developer’s computer to set the website up (ditto). What this means in practice is that we need never specify particular user accounts in our tests, or have particular content already set up on our development copy of the website. Behat can prepare content and accounts for us, ready for our tests to then make use of them.

A successful run by Behat results in a screen full of literally green lights: each line of the scenario goes green if Behat both understands it and also can actually fulfil it: click on this link; or put this text into this input box. However, if anything was either broken or not yet written, the developer would receive clear red alerts that action was required.

We were also able to extend Behat’s knowledge of what constitutes a comprehensible action on a website. It already knew about clicking links, or hitting submit buttons, but a key requirement was to get it to understand RSS, the format for syndicating content on the web. We were able to do this very quickly with custom PHP code.

In no time at all, we would have a new Gherkin requirement that had been interpreted by Behat, and showing lots of red warning lights: because by that point, it was only specified, not built! But at the same time, older functionality would still show us green lights, indicating that more recent work was not conflicting with the requirements of somewhat older work.

Building the functionality

We built out the functionality using other existing systems. We picked the RSS standard for syndicating data, and Drupal has very good support for both consuming this standard from remote websites (using the Feeds module) and also repackaging it for consumption by other websites (using Views and Views RSS). Because this was intended as an internal project, we also used a clear, plain, crisp administrative design throughout, provided by the Adminimal theme.

When it came to building each feature, once its scenario was specified in Gherkin syntax, most of the work was possible using Drupal content types, views and other configuration, which we were able to store alongside the codebase using the Features module. This allowed us to change configuration, and save our changes, and then always if necessary return to the previous state of configuration should any BDD tests no longer pass.

A few small customisations were necessary, but we could isolate these:

  1. When a website user was making the decision to re-syndicate content, on the same page as the content we needed to link to the exact remote RSS feed that was the source for the content.

  2. When the content was being re-syndicated from Forest Desk to another GCP website, not only did its content tagging need to be preserved (e.g. this content pertains to “Palm oil”) but the tagging needed to end up in the right vocabulary on the remote site (e.g. “Palm oil” is a commodity, not a country or piece of legislation). This required a custom extension to RSS.

  3. Similarly, when content tagged with geographical locations (e.g. longitude and latitude points) needed to be re-syndicated, the GeoRSS standard needed to be implemented to re-display the locations in the right format.

However, each customisation in effect supported a very specific piece of functionality; removing it only affected that piece, leaving the rest of the website functioning correctly.

Summary

Behaviour-driven development allowed us to specify and build a website quickly and within agile principles. It also meant that at the end of the project we had a successfully running test suite, that could be automated for peace of mind both during the acceptance phase but also for any future ongoing development. This means that changes of all sizes can be made with much greater confidence.

Moreover, the resulting suite of BDD tests is a living, breathing part of the website project in its own right, indirectly serving the site’s users by guaranteeing a minimum quality of experience and functionality. As the website itself grows, the suite will not just support the growth, but will be able to grow with it and become richer at the same time.

Questions

The Forest Desk is not publicly viewable but feel free to ask any questions you may have in the comments section below!

Comments

Excellent Web World (not verified)
Case study is important in every project.

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