The document discusses test-driven development (TDD) and how it provides consistent answers to questions about how to get started with testing code. It demonstrates TDD by walking through an example of writing tests and code to create a blog post. Key points made include: write tests before code; write one acceptance test and unit tests at a time; use test doubles in unit tests; and iterate between writing a test, making it pass by writing minimal code, then refactoring as needed. The process involves two "red-green-refactor" loops between acceptance and unit test levels.

1. Getting Answers to
Your Testing Questions
Josh Justice

2. CodingItWrong
CodingItWrong

3. @bignerdranch
bignerdranch.com

4. Ruby on Rails course
June 27–July 1
bit.ly/nerdrails

5. How do I get started
testing? 🤔

6. Questions! 🤔
• Do I write the test or production code first?
• What do I test first?
• How many acceptance/unit tests do I write?
• How much test code do I write at a time? Production code?
• Do I test every line of code and configuration?
• How much do I use test doubles? What do I test for?

7. Everyone agrees!
🙈

8. "Unit tests are good!"
"Unit tests are bad!"
"Mocks are good!"
"Mocks are bad!"
😩

10. What if we didn’t have
to worry about all those
questions at once?

11. Test-Driven
Development:
An approach to testing that
provides a consistent set of
answers to those questions.

12. “TDD is dead”…?

13. Too rigid?
• Not “follow this exactly or you’re a bad developer.”
• Not “this is the only way it can be done.”
• Give it a whole-hearted try. Then you’ll know when
to apply it and when not to.
• Or, just take a principle or two and see if they help.

14. Goals
• Show TDD applied to a small real-world example.
• Show how it answers those questions about how to
get started in testing.
• Motivate you to try it if you haven’t (or if you
haven’t strictly).

15. Not Goals
• Convince you testing is a good idea.
• Introduce testing concepts and terms.
• Provide rationale for individual points of TDD.

16. learntdd.in/rails

17. Requirement: as a
user, I want to be able
to create a blog post.
(of course)

18. Do I write the test or
production code first?
Write tests first.
🤔

19. Why tests first?
• To make sure there's time to test.
• To make sure your code is covered by tests.
• To make sure your code is easy to test.
• To let tests drive your design.

20. What do I test first?
Start outside the
system.
🤔

21. How much test do I
write at a time?
Write a whole
acceptance test
for one feature.
🤔

22. # spec/features/creating_a_blog_post_spec.rb
require 'rails_helper'
describe 'Creating a blog post' do
it 'saves and displays the resulting blog post' do
visit '/blog_posts/new'
fill_in 'Title', with: 'Hello, World!'
fill_in 'Body', with: 'Hello, I say!'
click_on 'Create Blog Post'
blog_post = BlogPost.order("id").last
expect(blog_post.title).to eq('Hello, World!')
expect(blog_post.body).to eq('Hello, I say!')
expect(page).to have_content('Hello, World!')
expect(page).to have_content('Hello, I say!')
end
end

23. # spec/features/creating_a_blog_post_spec.rb
require 'rails_helper'
describe 'Creating a blog post' do
it 'saves and displays the resulting blog post' do
visit '/blog_posts/new'
fill_in 'Title', with: 'Hello, World!'
fill_in 'Body', with: 'Hello, I say!'
click_on 'Create Blog Post'
blog_post = BlogPost.order("id").last
expect(blog_post.title).to eq('Hello, World!')
expect(blog_post.body).to eq('Hello, I say!')
expect(page).to have_content('Hello, World!')
expect(page).to have_content('Hello, I say!')
end
end How much do I use test doubles?
In acceptance tests,
don’t use test doubles.
🤔

24. Run the test and watch
it fail, to know what to
implement first.

25. # rspec spec/features/creating_a_blog_post_spec.rb
F
Failures:
1) Creating a blog post saves and displays the resulting blog
post
Failure/Error: visit '/blog_posts/new'
ActionController::RoutingError:
No route matches [GET] "/blog_posts/new"

26. # config/routes.rb
Rails.application.routes.draw do
resources :blog_posts
end

27. # config/routes.rb
Rails.application.routes.draw do
resources :blog_posts
end
Do I test every line?
No, you can fix
trivial errors directly.
🤔

28. # config/routes.rb
Rails.application.routes.draw do
resources :blog_posts
end
How much production code
do I write at a time?
Just enough to fix
the current error.
🤔

29. Red-Green-Refactor

30. A note on refactoring.

31. # rspec spec/features/creating_a_blog_post_spec.rb
F
Failures:
1) Creating a blog post saves and displays the resulting blog
post
Failure/Error: visit '/blog_posts/new'
ActionController::RoutingError:
uninitialized constant BlogPostsController

32. # app/controllers/blog_posts_controller.rb
class BlogPostsController < ApplicationController
end

33. # rspec spec/features/creating_a_blog_post_spec.rb
F
Failures:
1) Creating a blog post saves and displays the resulting blog
post
Failure/Error: visit '/blog_posts/new'
AbstractController::ActionNotFound:
The action 'new' could not be found for BlogPostsController

34. # app/controllers/blog_posts_controller.rb
class BlogPostsController < ApplicationController
def new
end
end

35. # rspec spec/features/creating_a_blog_post_spec.rb
F
Failures:
1) Creating a blog post saves and displays the resulting blog
post
Failure/Error: visit '/blog_posts/new'
ActionView::MissingTemplate:
Missing template blog_posts/new

36. <%# app/views/blog_posts/new.html.erb %>

37. # rspec spec/features/creating_a_blog_post_spec.rb
F
Failures:
1) Creating a blog post saves and displays the resulting blog
post
Failure/Error: fill_in 'Title', with: 'Hello, World!'
Capybara::ElementNotFound:
Unable to find field "Title"

38. <%# app/views/blog_posts/new.html.erb %>
<%= form_for @blog_post do |f| %>
<div>
<%= f.label :title %>
<%= f.text_field :title %>
</div>
<div>
<%= f.label :body %>
<%= f.text_area :body %>
</div>
<%= f.submit 'Create Blog Post' %>
<% end %>

39. <%# app/views/blog_posts/new.html.erb %>
<%= form_for @blog_post do |f| %>
<div>
<%= f.label :title %>
<%= f.text_field :title %>
</div>
<div>
<%= f.label :body %>
<%= f.text_area :body %>
</div>
<%= f.submit 'Create Blog Post' %>
<% end %>
How much production code
do I write at a time?
Sometimes, more than enough
to fix the current error.
🤔

40. # rspec spec/features/creating_a_blog_post_spec.rb
F
Failures:
1) Creating a blog post saves and displays the resulting blog
post
Failure/Error: <%= form_for @blog_post do |f| %>
ActionView::Template::Error:
First argument in form cannot contain nil or be empty

41. # rspec spec/features/creating_a_blog_post_spec.rb
F
Failures:
1) Creating a blog post saves and displays the resulting blog
post
Failure/Error: <%= form_for @blog_post do |f| %>
ActionView::Template::Error:
First argument in form cannot contain nil or be empty
When do I write unit tests?
Step down to a unit test when
there are behavioral errors.
🤔

42. Why unit test when there's
already an acceptance test?

43. Acceptance tests
demonstrate external
quality: whether the
system works.

44. Acceptance tests don't
demonstrate internal
quality: whether the
code is maintainable.

45. Unit tests expose internal
quality. They drive design.

46. # spec/controllers/blog_posts_controller_spec.rb
require 'rails_helper'
describe BlogPostsController do
describe '#new' do
it 'returns a blog post' do
blog_post = instance_double(BlogPost)
expect(BlogPost).to receive(:new).and_return(blog_post)
get :new
expect(assigns[:blog_post]).to eq(blog_post)
end
end
end

47. # spec/controllers/blog_posts_controller_spec.rb
require 'rails_helper'
describe BlogPostsController do
describe '#new' do
it 'returns a blog post' do
blog_post = instance_double(BlogPost)
expect(BlogPost).to receive(:new).and_return(blog_post)
get :new
expect(assigns[:blog_post]).to eq(blog_post)
end
end
end
How much test do I write?
Write only enough unit test to
expose the behavioral error.
🤔

48. # spec/controllers/blog_posts_controller_spec.rb
require 'rails_helper'
describe BlogPostsController do
describe '#new' do
it 'returns a blog post' do
blog_post = instance_double(BlogPost)
expect(BlogPost).to receive(:new).and_return(blog_post)
get :new
expect(assigns[:blog_post]).to eq(blog_post)
end
end
end
How much test do I write?
Specify one behavior per
unit test case.
🤔

49. # spec/controllers/blog_posts_controller_spec.rb
require 'rails_helper'
describe BlogPostsController do
describe '#new' do
it 'returns a blog post' do
blog_post = instance_double(BlogPost)
expect(BlogPost).to receive(:new).and_return(blog_post)
get :new
expect(assigns[:blog_post]).to eq(blog_post)
end
end
end
How much do I use test doubles?
In unit tests, use test doubles
in place of any collaborators.
🤔

50. # spec/controllers/blog_posts_controller_spec.rb
require 'rails_helper'
describe BlogPostsController do
describe '#new' do
it 'returns a blog post' do
blog_post = instance_double(BlogPost)
expect(BlogPost).to receive(:new).and_return(blog_post)
get :new
expect(assigns[:blog_post]).to eq(blog_post)
end
end
end
What do I test for?
In unit tests, behavior, not
state. (Mostly.)
🤔

51. # rspec spec/controllers/blog_posts_controller_spec.rb
F
Failures:
1) BlogPostsController#new returns a blog post
Failure/Error: blog_post = instance_double(BlogPost)
NameError:
uninitialized constant BlogPost

52. # db/migrate/20160223100510_create_blog_posts.rb
class CreateBlogPosts < ActiveRecord::Migration
def change
create_table :blog_posts do |t|
t.string :title
t.text :body
end
end
end
# app/models/blog_post.rb
class BlogPost < ActiveRecord::Base
end

53. # rspec spec/controllers/blog_posts_controller_spec.rb
F
Failures:
1) BlogPostsController#new returns a blog post
Failure/Error: expect(assigns[:blog_post]).to eq(blog_post)
expected: #<InstanceDouble(BlogPost) (anonymous)>
got: nil
(compared using ==)

54. # app/controllers/blog_posts_controller.rb
class BlogPostsController < ApplicationController
def new
@blog_post = BlogPost.new
end
end

55. # rspec spec/controllers/blog_posts_controller_spec.rb
.
Finished in 0.03134 seconds (files took 1.46 seconds to load)
1 example, 0 failures

56. How often do I run which
tests?
When the unit test
passes, step back up
to the acceptance test.
🤔

57. Two Red-Green-
Refactor Loops

58. # spec/features/creating_a_blog_post_spec.rb
require 'rails_helper'
describe 'Creating a blog post' do
it 'saves and displays the resulting blog post' do
visit '/blog_posts/new'
fill_in 'Title', with: 'Hello, World!'
fill_in 'Body', with: 'Hello, I say!'
click_on 'Create Blog Post'
blog_post = BlogPost.order("id").last
expect(blog_post.title).to eq('Hello, World!')
expect(blog_post.body).to eq('Hello, I say!')
expect(page).to have_content('Hello, World!')
expect(page).to have_content('Hello, I say!')
end
end

59. # rspec spec/features/creating_a_blog_post_spec.rb
F
Failures:
1) Creating a blog post saves and displays the resulting blog
post
Failure/Error: click_on 'Create Blog Post'
AbstractController::ActionNotFound:
The action 'create' could not be found for
BlogPostsController

60. # app/controllers/blog_posts_controller.rb
class BlogPostsController < ApplicationController
def new
...
end
def create
end
end

61. # rspec spec/features/creating_a_blog_post_spec.rb
F
Failures:
1) Creating a blog post saves and displays the resulting blog
post
Failure/Error: click_on 'Create Blog Post'
ActionView::MissingTemplate:
Missing template blog_posts/create

62. <%# app/views/blog_posts/create.html.erb %>

63. # rspec spec/features/creating_a_blog_post_spec.rb
F
Failures:
1) Creating a blog post saves and displays the resulting blog
post
Failure/Error: expect(blog_post.title).to eq('Hello, World!')
NoMethodError:
undefined method `title' for nil:NilClass

64. # spec/controllers/blog_posts_controller_spec.rb
require 'rails_helper'
describe BlogPostsController do
describe '#new' do
...
end
describe '#create' do
it 'creates a blog post record' do
expect(BlogPost).to receive(:create).with(title: 'My Title',
body: 'My Body')
post :create, {
blog_post: {
title: 'My Title',
body: 'My Body',
}
}
end
end
end

65. # rspec spec/controllers/blog_posts_controller_spec.rb
.F
Failures:
1) BlogPostsController#create creates a blog post record
Failure/Error:
expect(BlogPost).to receive(:create).with(title: 'My Title',
body: 'My Body')
(BlogPost(id: integer, title: string, body: text)
(class)).create({:title=>"My Title", :body=>"My Body"})
expected: 1 time with arguments: ({:title=>"My
Title", :body=>"My Body"})
received: 0 times

66. # app/controllers/blog_posts_controller.rb
class BlogPostsController < ApplicationController
...
def create
BlogPost.create(params[:blog_post])
end
end
☝😧 Wait for iiiiiiiit…

67. # rspec spec/controllers/blog_posts_controller_spec.rb
..
Finished in 0.02774 seconds (files took 1.53 seconds to load)
2 examples, 0 failures

68. # rspec spec/features/creating_a_blog_post_spec.rb
F
Failures:
1) Creating a blog post saves and displays the resulting blog
post
Failure/Error: BlogPost.create(params[:blog_post])
ActiveModel::ForbiddenAttributesError

69. # app/controllers/blog_posts_controller.rb
class BlogPostsController < ApplicationController
...
def create
BlogPost.create(blog_post_params)
end
private
def blog_post_params
params.require(:blog_post).permit(:title, :body)
end
end

70. # rspec spec/features/creating_a_blog_post_spec.rb
F
Failures:
1) Creating a blog post saves and displays the resulting blog
post
Failure/Error: expect(page).to have_content('Hello, World!')
expected to find text "Hello, World!" in ""

71. <%# app/views/blog_posts/create.html.erb %>
<h1><%= @blog_post.title %></h1>
<div>
<%= @blog_post.body %>
</div>

72. # rspec spec/features/creating_a_blog_post_spec.rb
F
Failures:
1) Creating a blog post saves and displays the resulting blog
post
Failure/Error: <h1><%= @blog_post.title %></h1>
ActionView::Template::Error:
undefined method `title' for nil:NilClass

73. # spec/controllers/blog_posts_controller_spec.rb
require 'rails_helper'
describe BlogPostsController do
...
describe '#create' do
it 'creates a blog post record' do
...
end
it 'returns the new blog post to the view' do
blog_post = instance_double(BlogPost)
allow(BlogPost).to receive(:create).and_return(blog_post)
post :create, {
blog_post: {
title: 'My Title',
body: 'My Body',
}
}
expect(assigns[:blog_post]).to eq(blog_post)
end
end
end

74. # rspec spec/controllers/blog_posts_controller_spec.rb
..F
Failures:
1) BlogPostsController#create returns the new blog post to the
view
Failure/Error: expect(assigns[:blog_post]).to eq(blog_post)
expected: #<InstanceDouble(BlogPost) (anonymous)>
got: nil
(compared using ==)

75. # app/controllers/blog_posts_controller.rb
class BlogPostsController < ApplicationController
...
def create
@blog_post = BlogPost.create(blog_post_params)
end
...
end

76. # rspec spec/controllers/blog_posts_controller_spec.rb
...
Finished in 0.03122 seconds (files took 1.52 seconds to load)
3 examples, 0 failures
# rspec
....
Finished in 0.17293 seconds (files took 1.49 seconds to load)
4 examples, 0 failures
# rspec spec/features/creating_a_blog_post_spec.rb
.
Finished in 0.15204 seconds (files took 1.42 seconds to load)
1 example, 0 failures

77. # spec/controllers/blog_posts_controller_spec.rb
require 'rails_helper'
describe BlogPostsController do
...
describe '#create' do
it 'creates a blog post record' do
expect(BlogPost).to receive(:create).with(title: 'My Title',
body: 'My Body')
post :create, {
blog_post: {
title: 'My Title',
body: 'My Body',
}
}
end
it 'returns the new blog post to the view' do
blog_post = instance_double(BlogPost)
allow(BlogPost).to receive(:create).and_return(blog_post)
post :create, {
blog_post: {
title: 'My Title',
body: 'My Body',
}
}
expect(assigns[:blog_post]).to eq(blog_post)
end
end
end

78. # spec/controllers/blog_posts_controller_spec.rb
require 'rails_helper'
describe BlogPostsController do
...
describe '#create' do
let(:post_params) {
{
blog_post: {
title: 'My Title',
body: 'My Body',
}
}
}
it 'creates a blog post record' do
expect(BlogPost).to receive(:create).with(title: 'My Title',
body: 'My Body')
post :create, post_params
end
it 'returns the new blog post to the view' do
blog_post = instance_double(BlogPost)
allow(BlogPost).to receive(:create).and_return(blog_post)
post :create, post_params
expect(assigns[:blog_post]).to eq(blog_post)
end
end
end

79. # rspec
....
Finished in 0.17293 seconds (files took 1.49 seconds to load)
4 examples, 0 failures

80. Imagine if testing the way
you want to was second-
nature.

81. TDD can help you
get there.
…whether you end up embracing all of it or not.

82. 🤔 Questions?

83. To Learn More
• learntdd.in/rails
• The RSpec Book
• Growing Object-Oriented Software, Guided By
Tests

84. Thanks! 🙃
@CodingItWrong
learntdd.in/rails