tdd with rails

TDD with RailsAndrzejKrzywda.com

RuPy 2008Poznan, Poland

Who am I?

Andrzej Krzywda

• Developing software since 2000

• Java/.NET/PHP/Python/Rails

Now mostly Rails

First Rails app in November 2004

I started doing TDD in 2001

Also involved in a project called Resolver

One, written in IronPython

Started a Rails company in 2007

Test Driven Development

The goals in a software project

Requirements are goals

What helps in achieving goals?

Goal visualization

Software requirements

TDD (in a high level) is about visualizing goals.

Software developers are responsible

for visualization of other people goals

What is TDD?

TDD is about writing tests BEFORE writing

production code.

What kind of tests?

Be pragmatic.

TDD definitions

TDD is like politics or religion

Everyone thinks he’s right

I think they are wrong...

My TDD

Acceptance tests

+Unit tests

Acceptance tests + Unit tests

Definitions

Acceptance test is a test from the user’s

perspective.

Unit test is a test for a class.

Which are more important?

It depends.

0

25

50

75

100

2001 2003 2006 2008

Unit tests Acceptance tests

The level of test coverage

Java IronPython Rails

Why?

Why

• Rails is a more mature community (in the TDD aspect)

• So many great tools

• REST! - almost no need to test controllers

• Almost only model unit tests

• Acceptance tests, trivial with RSpec Stories + Webrat

Acceptance tests

Doing TDD means to have many tests.

TDD is a good requirements

management technique

TDD

• 3 x D rule

• Defense (Tests)

• Design

• Documentation

???

Let’s take an example.

A blog application

We are about to add a ‘commenting’ feature.

How can we visualize it?

As a Rails developer?

> script/generate migration CreateCommentsTable content:text

class Post < ActiveRecord::Base has_many :commentsend

class Comment < ActiveRecord::Base belongs_to :postend

<%= render_collection @post.comments %>

As a software developer?

$$$$

Someone pays for your work, right?

What users are involved in the blog commenting

feature?

A blog reader

As a blog reader

I want to comment on a blog post

So that I can share my thoughts on the topic

A blog owner / author

As a blog ownerI want to display

commentsSo that other people can see how cool my

blog is.

As a blog ownerI want to moderate

commentsSo that there is no spam

As a blog ownerI want to display captcha

imagesSo that there is no spam

Another blog reader

As another blog readerI want to reply to other

commentsSo that I can prove they

are wrong

As an RSS subscriber...

As a bad person...

As a bad personI want to use SQL InjectionSo that I can break your blog and become famous.

The structure

Spikes / prototyping

User stories

Show your customer the user stories.

Discuss it.

Estimate it.

Prioritize.

Implement it.

Split it into tasks which are usually related to

scenarios.

TDD helps you focusing on one task at a time.

There’s always exactly one test failing.

Tools

RSpec storiesWebrat

Selenium RCWatir

RSpec / BDD

RSpec stories != RSpec examples

RSpec stories is for acceptance tests

‘RSpec examples’ is a unit testing tool.

The process

List the scenarios.

RSpec storyStory: Commenting on a blog

As a blog reader I want to comment So that I can share my thoughts about the article Scenario: Simple adding of a comment

Given an existing blog post And a blog reader writing a comment When he submits it Then it appears below the blog post

stories/comments

require File.join('stories', 'helper')

steps_for :comments doend

with_steps_for :comments do run 'stories/comments', :type => RailsStoryend

require File.join('stories', 'helper')

steps_for :comments do Given "an existing blog post" do @post = Post.create(:title => 'title', :body => 'body') endend

with_steps_for :comments do run 'stories/comments', :type => RailsStoryend

require File.join('stories', 'helper')

steps_for :comments do Given "an existing blog post" do @post = Post.create(:title => 'title', :body => 'body') end Given "a blog reader writing a comment" do visits '/' clicks_link 'Read more...' fills_in 'comment[content]', :with => 'First!' endend

RSpec story runnerrequire File.join('stories', 'helper')

steps_for :comments do Given "an existing blog post" do @post = Post.create(:title => 'title', :body => 'body') end Given "a blog reader writing a comment" do visits '/' clicks_link 'Read more...' fills_in 'comment[content]', :with => 'First!' end

stories/comments.rb

RSpec story runner When "he submits it" do clicks_button "Add" end Then "it appears below the blog post" do visits '/' clicks_link 'Read more...' response.body.should have_text 'First!' end

end with_steps_for :comments, :posts do run 'stories/comments', :type => RailsStoryend

stories/comments.rb

Run the test

It fails

Implement one step at a time

If it’s not trivial start with a spec first.

RSpec example

• Bryan Helmkamp

• github.com/brynary/webrat

• manipulates DOM

• builds POST from DOM

Webrat

Problems?

Slow builds

Fragile, unreliable tests

What about the scientists opinions?

Thirumalesh Bhat and Nachiappan Nagappan. Evaluating the efficacy of test- driven development: industrial case studies. In ISESE ’06: Proceedings of the 2006 ACM/IEEE international symposium on Empirical software engineering, pa- ges 356–363, New York, NY, USA, 2006. ACM.

Gerardo Canfora, Aniello Cimitile, Felix Garcia, Mario Piattini, and Corrado Aaron Visaggio. Evaluating advantages of test driven development: a controlled experi- ment with professionals. In ISESE ’06: Proceedings of the 2006 ACM/IEEE inter- national symposium on Empirical software engineering, pages 364–371, New York, NY, USA, 2006. ACM.

Steven Fraser, Dave Astels, Kent Beck, Barry Boehm, John McGregor, James New- kirk, and Charlie Poole. Discipline and practices of tdd: (test driven development). In OOPSLA ’03: Companion of the 18th annual ACM SIGPLAN conference on Object-oriented programming, systems, languages, and applications, pages 268–270, New York, NY, USA, 2003. ACM.

Ivana Turnu, Marco Melis, Alessandra Cau, Michele Marchesi, and Alessio Setzu. Introducing tdd on a free libre open source software pro ject: a simulation expe- riment. In QUTE-SWAP ’04: Proceedings of the 2004 workshop on Quantitative techniques for software agile process, pages 59–65, New York, NY, USA, 2004. ACM.

What are the consequences of doing

TDD?

I don’t use debuggers.

Simpler, thus better design

Frequently asking the question:

“How would I test it?”

After many years of doing TDD, I find it

VERY difficult to work with untested code.

Unit testing tips

• One assertion per test method

• Write the assertion first

• Thin controllers, fat models

• REST

• Fixtures, it’s easier without them

• Specs output as a documentation

Quotes

“TDD was the single most effective software

development habit I adopted”

“My impression is that it's intuitive the way riding a bicycle is intuitive. Extremely UN-intuitive for the child who is learning, but to the adult hardly anything but common sense and difficult to unlearn.

That said, as a developer who's fallen down and scraped his knee... since I need to get from point A to point B fast, I know how to run already so I still do that.”

“TDD doesn't work very well when you're

trying to work on something new - try a

spike instead, and follow with test-driven coding

later”

“It’s not clear how to split tests into suites”

“TDD is intuitive once you start doing it”

“You have to start thinking in a different

way”

“TDD is only one thing, don’t forget about the

others: refactoring, code quality”

“Writing good tests may be difficult for

beginners”

“I can’t achieve a 100% code coverage”

My thoughts

A different way of thinking

I always think “How can I test that” instead of

“how do I implement it”

Live coding

Thank you!

• http://AndrzejKrzywda.com

• Rails consulting, training

• Feel free to email/IM me with TDD questions

• andrzejkrzywda@gmail.com