How BDD focusses on the ‘why’

Today i got talking with somebody who was unconvinced of the benefits of behaviour driven development. I hope i’m not misquoting them, but they seemed to be saying that BDD doesn’t tell you why something happens, only what happens.

This person also said that BDD doesn’t encourage you to code correctly. That i agree with. You can code poorly with any test tools or development framework. The only thing that’s going to encourage you to code cleanly is your own standards, or those that are instilled into you by requirement, or pair programming, or code review.

To me, the focus on the why is a key difference of BDD as opposed to TDD. Here’s an example for comparison:

Test First Development tells you that you’re going to use an Array of names and it’s going to receive the shuffle method. You write the test because you’ve already decided that’s what you’re going to do. It is brittle because a change in the code will require you to rewrite the test.

Test Driven Development says that somehow some names are going to be input, and after the process they’ll come out in a random order. It doesn’t necessarily mind whether you use an Array, Hash, a shuffle method or write your own randomising function. You let the tests drive you to make those decisions when you need to.

Behaviour Driven Development tells you about me as a key stakeholder, and that i want to draw names in a random order, so that i can assign prizes fairly. It tells a story about the people entering, explaining in natural language that the names are drawn out of a hat, and when they are, the first randomly chosen person picked gets the first prize, and their name is put aside so that they don’t win another prize. How you implement the details to achieve this behaviour is entirely up to you as a developer. But you should understand quite well what you’re expecting to achieve, and why.

Okay, i know, it’s a horrible example because it’s quite difficult to test for randomness. Given an unbiased coin / When i flip the coin / Then i should get … either heads or tails … Anyway, hopefully those examples show how i consider the test methodologies to differ.

My mentor Enrique recently helped me to understand BDD, particularly Cucumber scenarios, as documentation of the understanding between the client and the developer. It just so happens that you can execute this documentation to help you write your code, and continue to use it for regression testing.

Now i pass over to you, my readers! Are your opinions different from mine? What have i missed out, misunderstood, or misrepresented? I’m not an expert here! Fortunately, you don’t need to be a BDD expert to benefit from using it! :)

Pretty autospec growl messages

It’s interesting how you can sometimes notice something through someone else’s eyes that you’d previously overlooked. This week i have been mostly working with my apprentice Despo on a Rails project. Despo noticed that running specs in Rails takes a long time to initialize, which something i am well aware of but i guess i’ve sort of got used to it.

So we decided to do something about it. The first thing we did was set up Spork. If you want to know how to do that i recommend this post by Chris: How to get Spork working NOW on Rails 3, Rspec 2 and Cucumber.

As Chris mentioned at the end of that post, autotest and autotest-growl play well with Spork, so that is what we did next. The results can be quite nice!

Autotest notices which files have changed and starts running the relevant specs:

Autotest notices modifications

Growl can be configured to show failure messages in red:

Growl can be configured to show failure messages in red

Success messages are shown in green:

Success messages are shown in green

Growl can also show when specs are pending:

Growl can also show when specs are pending

How did we achieve this?

Firstly you will need to install the gems autotest and autotest-growl. Either include them in a bundle, or install them system-wide if you want to use them across all projects.

If you use RVM for different versions of ruby you might find this command useful:

for version in $(rvm list strings); do rvm use $version@global && gem install autotest && gem install autotest-growl; done

Secondly you will need a .autotest file. You can either put it in your project’s root directory, or in your home directory ~/.autotest

Here is mine so you can see what it looks like:

#!/usr/bin/env ruby
require 'rubygems'
require 'autotest/growl'

Autotest::Growl::image_dir = File.join(ENV['HOME'], '.autotest_images')
Autotest::Growl::show_modified_files = true

Autotest.add_hook :initialize do |autotest|
  %w(.git .DS_Store db log tmp).each do |exception|
    autotest.add_exception(exception)
  end
  autotest.order = :random
end

Thirdly you will need to install Growl and configure it to your liking. I have mine set to Music Video because it’s so impossible to miss!

The only trouble with the Music Video style is it can only display one message at a time, so i make it fade in and last for just 1 second. Happily, with growl colouring, you don’t really need to read the message – the colour tells you immediately what happened.

The colours you need to set are:

  • Very Low for passed
  • Moderate for pending
  • Normal for info
  • Emergency for failed (or syntax error)

Here is my Growl configuration:

Here is my Growl configuration

Finally, if you want cute pictures to come up with your growl messages, you simply need to put them in ~/.autotest_images – named passed.png, pending.png, info.png, failed.png and error.png.

These are my autotest images

Running autotest

Now, of course, you need to know how to run it!

With Rails 3 you need

AUTOFEATURE=true autotest

With Rails 2 it’s

AUTOFEATURE=true autospec

If you only want to run specs and not features, just take away the AUTOFEATURE=true bit.

But what about FSEvent?

The normal behaviour for autotest is to constantly poll your filesystem looking for changes. This is wasteful as it will use a lot of CPU and drain your battery, but there is an alternative. From Mac OSX 10.5 onwards an FSEvent service reports modified files.

To make use of FSEvent, you should be able to just install the autotest-fsevent gem and require 'autotest/fsevent' in your .autotest file.

Unfortunately, when i tried it, the mere presence of the autotest-fsevent gem seems to cause the specs not to run. It notices changes but doesn’t do anything about them. So if anyone can help me to understand what’s up with that, i would be grateful!

In the mean time, i’m just trying to remember to stop autotest whenever i’ve finished using it.