Test Driven Development Lifecycle

Start at the top level with a user requirement. This will ensure that you are trying to solve the right problem in the first place.

Cucumber / Steak

Write a simple high level requirement in cucumber or steak. For example if you were writing an api and you wanted to allow people to post activity.

First you would write out the requirement in plain english.

Feature: Creating activity
  As an activity producer
  I want to post activity to the api
  In order to share it with the world

  Scenario: POST to /activity
    Given I am an authorized activity producer
    When I post some activity
    Then I should receive a 200 success status

This defines the high level picture of what the application aims to achieve. From this point the next step is to write some steps to properly test that the features are working.

Obviously the features won’t be working yet, because that’s not how test/behaviour/real-world driven development works. If you start writing code before you really know what you are building, then it is likely that you will at some point, perhaps without realising, implement the wrong feature. More likely though, being that smart martin that you are, you will implement the correct feature, but unwittingly leave a bug in it. No harm, you say, bugs happen in software and it’s probably only one line of code that needs changing. But if the bug doesn’t manifest itself for a few days, weeks, months, then it will take an ever increasing amount of time for you to track it down. Then once you have isolated it, you have to ensure it won’t happen again.

This all comes down to testing. If you can easily run a bank of tests that confirm that your application is behaving at night you will, infact, sleep better at night. For some this is reason enough to write tests, but wait, there’s more. If you have a comprehensive collection of tests you can use to verify that your application is working correctly, then you are in a very good position to do some refactoring. No more worrying if you’ve broken some seemingly unrelated piece of functionality when you make a change to the application.

Controller tests

The next layer down the stack is the controller, this makes sense, since this is the layer that manages incoming requests. So after writing the initial acceptance test in a high level language, then implementing the steps necessary to test this logic in a slightly lower level language, you now drop down to a relativly granular level. This is where you start to stub out the main functionality of the application. So in the case of our activity example above, you would at this stage be stubbing out the functionality of the models, and just dealong with the way that controllers handle requests.

This layer may be preceeded by another, slightly higher level one in which the routing for the application is set up, however this is quite a web application specific area.

Model tests

The model tests are the core of the testing universe, they are very small, low level details about the various methods that a model provides.

The model tests are the most important tests, as they contain the business logic for your application. But they are often also the easiest tests to write. This is because a lot of the time you will be dealing with primitive data types. No external services to worry about. This is a good reason to push as much logic into the model as possible, it is far easier to test this that it is to put it in your controller then try to stub it out.

Other tests

All of this testing malarkey is great and everything, but sometimes you have got to just use the product to uncover random bugs, but don’t worry, that’s not to say we can’t still use testing to help us. Instead of jumping right in and fixing that bug like a good boy scout hacker, write a failing test that reproduces the bug. This test may exists as (m)any layer(s) of the test stack. Often you will need to write a test in the acceptance layer to perform the same interaction that caused the bug, then once that has caught the bug, go down the layers and write tests for the code paths that the bug touches, these failing tests will then (all going to plan) be green once you have fixed the bug, and as a billy bonus you’ve got yourself another test or two that will ensure many good nights sleep in the future.

Final thoughts

The testing pattern of development is still not used as a default development technique. Many (most) tutorials you find out there will focus on the functionality that they are trying to tutor you on, but a vital part of implementing any functionality is to ensure a long lifespan by testing it thoroughly.

Testing will seem like a chore at first, but once you get the hang of it, the whole process becomes a pattern, that if followed with a small bit of dicipline, will lead you to enlightenment, it will allow you to model your ideas with more structure with the tools available.

In many ways it’s like learning a new language, with more languages, you see more ways of doing things. With testing, you’ll see new ways to express your applications logic using high level language.