Introducing BravoDelta: Erlang BDD based on Cucumber

I highly recommend Armstrong's Programming Erlang

I ❤ Erlang.  I learned about Erlang while simultaneously playing w/ CouchDB (written in Erlang) and reading Siebel’s excellent Coders At Work interview of Erlang creator Joe Armstrong.  Erlang takes me back to my lisp and prolog days – it’s interesting, powerful and elegant.  Even better, it’s performant, time tested and proven.

To whet my Erlang skills, I decided to port of the most essential development tools I’ve used: Cucumber BDD.  I think that using BDD is one of the most critical success criteria for a project that wants to move quickly and respond to customers.  If you’d like to see Cucumber in action, check out my WhatTheBus project.  A Cucumber test is written in “simple English” and looks like this:

Scenario: Web Page1
    When I go to the home page.
    Then I should see "Districts".

To run Bravo Delta, you’ll need Erlang installed on your system.  You may also want to setup the WhatTheBus project because the initial drop uses that RoR web site as it’s target.  I’ve uploaded the code onto GitHub project BravoDelta (code contributions welcome).

NOTE: This is a functional core – it is not expected to be a complete Cuke replacement at this point!

The code base consists of the following files:

  • bdd.erl (main code file, start using bdd:test(“scenario”).)
  • bdd.config (config file)
  • bdd_webrat.erl (standard steps that are used by many web page tests)
  • bravodelta.erl (same custom steps, must match feature file name)
  • bravodelta.feature (BDD test file)
  • bdd_utils.erl (utilities called by bdd & webrat)
  • bdd_selftest.erl (unit tests for utils – interesting pattern for selftest in this file!)
  • (data for unit tests)

Erlang makes parsing the feature file very easy.  Unlike Cucumber, there is no RegEx craziness because Erlang has groovy pattern matching.  Basically, each step decomposes into a single line starting with Given, When, or Then.  The code is designed so that developers can easily add custom steps and there are pre-built steps for common web tasks in the “webrat” step file.  A step processor looks like this in Erlang:

step(_Config, _Given, {step_when, _N, ["I go to the home page"]}) ->
	bdd_utils:http_get(_Config, []);
step(_Config, _Result, {step_then, _N, ["I should see", Text]}) ->

The steps are called by an Erlang recursive routine in BDD for each scenario in the feature file.  Explaining that code will have to wait for a future post.

The objective for Bravo Delta is to demonstrate simple Erlang concepts.  I wanted to make sure that the framework was easy to extend and could grow overtime.  My experience with Erlang is that my code generally gets smaller and more powerful as I iterate.  For example, moving from three types of steps (given_, when_, then_) to a single step type with atoms for type resulted in a 20% code reduction.

I hope to use it for future BDD projects and grow its capability because it is fast and simple to extend – I found Cucumber to be very slow.  It should also be possible to execute features in parallel with minimal changes to this code base.  That makes Bravo Delta very well suited to large projects with lots of tests and automated build systems.

This entry was posted in BravoDelta, Development, Quality by Rob H. Bookmark the permalink.

About Rob H

A Baltimore transplant to Austin, Rob thinks about ways of building scale infrastructure for the clouds using Agile processes. He sat on the OpenStack Foundation board for four years. He co-founded RackN enable software that creates hyperscale converged infrastructure.

7 thoughts on “Introducing BravoDelta: Erlang BDD based on Cucumber

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