RSpec ⛑

Formatting
Fixtures
Assertion
DRY-ing up tests
Test Doubles
- Stubbing HTTP requests

To test Rails applications, we prefer using RSpec over MiniTest but restrain ourselves to its core features and use the following best practices.

All general testing best practices and Web testing best practices apply to RSpec but working with a framework adds another superset of conventions to follow.

Formatting

Use a single, top-level describe ClassName block, with appropriate type.

RSpec.describe SomeClass, type: model do; end
RSpec.describe SomeClass, type: system do; end

Order validation, association, and method tests in the same order that they appear in the class.
Use describe to group tests by method-under-test.
1. Use . (or ::) when referring to a class method’s name.
2. Use # when referring to an instance method’s name.
describe 'the confirm method of User' describe 'search method of User'
describe '#confirm' describe '.search'

Use context to describe testing preconditions. context block descriptions should always start with ‘when’ or ‘given’, and be in the form of a sentence with proper grammar.

it 'processes payment if the params are valid'
it 'declines payment if the params are invalid'

context 'when params are valid' do
  it 'processes payment if the params are valid'
end

context 'when params are invalid' do
  it 'declines payment'
end

Use subject blocks to define objects for use in one-line specs only.

context 'when using an explicit subject' do
  subject { 'foo' }

  it 'should equal foo' do
    # it's not okay to use `subject` here:
    expect(subject).to eq('foo')
  end
end

context 'when defining a subject' do
  # it's okay to define a `subject` here:
  subject { 'foo' }

  it { expect(subject).to eq('foo') }
end

Put one-liner specs at the beginning of the outer describe blocks.

RSpec.describe 'validations' do
  it 'validates uniqueness of name' do
    Fabricate(:place, name: 'Bangkok')

    place_with_same_name = Fabricate.build(:place, name: 'Bangkok')

    expect(place_with_same_name).not_to be_valid
  end

  it { is_expected.to validate_presence_of(:name) }
  it { is_expected.to validate_presence_of(:slug) }
end

RSpec.describe 'validations' do
  it { is_expected.to validate_presence_of(:name) }
  it { is_expected.to validate_presence_of(:slug) }

  it 'validates uniqueness of name' do
    Fabricate(:place, name: 'Bangkok')

    place_with_same_name = Fabricate.build(:place, name: 'Bangkok')

    expect(place_with_same_name).not_to be_valid
  end
end

Always use the expect syntax.

it 'creates a resource' do
  response.should respond_with_content_type(:json)
end

it 'creates a resource' do
  expect(response).to respond_with_content_type(:json)
end

Don’t prefix it block descriptions with should. Use the imperative tone instead.
it 'should process payment'
it 'processes payment'
should is an artifact from a older Rspec version (< 3)

Do not leave line breaks after context or describe blocks.

RSpec.describe Place, type: :model do

  describe '#create' do

    it 'creates a place' do

      # ...
    end
  end
end

RSpec.describe Place, type: :model do
  describe '#create' do
    it 'creates a place' do
      # ...
    end
  end
end

Leave one line return around it blocks.

describe '#summary' do
  it 'returns the summary' do
    # ...
  end
  it 'does something else' do
    # ...
  end
  it 'does another thing' do
    # ...
  end
end

describe '#summary' do
  it 'returns the summary' do
    # ...
  end

  it 'does something else' do
    # ...
  end

  it 'does another thing' do
    # ...
  end
end

Fixtures

Factories

Use a gem like fabrication or factory_bot to reduce the verbosity when working with models.

user = User.create(name: 'Genoveffa',
                   surname: 'Piccolina',
                   city: 'Billyville',
                   birth: '17 August 1982',
                   active: true)

user = Factory.create(:user)

Fixtures isolation

DO NOT use let, let! to create fixtures and limit usage of before and after.

Instead, each test must create its own fixtures and setup.

RSpec.describe Article do
  # arrange
  let(:user) { FactoryGirl.create(:user) }

  before do
    # arrange
  end

  after do
    # cleanup
  end

  describe '#summary' do
    # act
    # assertion
  end
end

RSpec.describe Article do
  describe '#summary' do
    # arrange
    user = FactoryGirl.create(:user)

    # act

    # assertion
  end
end

Keep creation of fixtures to a minimum

Test suites can become very slow due to haphazard fixtures creation.

Try to make the tests atomic and as such avoid unnecessary fixtures creations.

it 'updates the cache counter' do
  place = Fabricate(:place)
  # Unnecessary creation of 5 records
  Fabricate.times(5, :checkin, place: place)

  expect(place.checkins_count).to eq 5
end

it 'updates the cache counter' do
  place = Fabricate(:place)
  Fabricate(:place, :checkin, place: place)

  expect(place.checkins_count).to eq 1
end

Assertion

Single expectation test

Each test should make only one assertion.

it 'creates a resource' do
  expect(response).to respond_with_content_type(:json)
  expect(response).to assign_to(:resource)
end

it { is_expected.to respond_with_content_type(:json) }
it { is_expected.to assign_to(:resource) }

For integration tests, sometimes the tests may suffer a performance hit especially when setup is complex. In those cases, it’s fine to assert more than one behavior.

Test all possible cases

Use Boundary value analysis technique to test valid, edge and invalid cases.

Split-up method’s input or object’s attributes into valid and invalid partitions and test both of them and their boundaries.

RSpec.describe '#month_in_english' do
  context 'when valid' do
    it 'returns "January" for 1' # lower boundary
  end
  context 'when invalid' do
    it 'returns nil for 0'
  end
end

RSpec.describe '#month_in_english' do
  context 'when valid' do
    it 'returns "January" for 1' # lower boundary
    it 'returns "March" for 3'
    it 'returns "December" for 12' # upper boundary
  end
  context 'when invalid' do
    it 'returns nil for 0'
    it 'returns nil for 13'
  end
end

Incidental State

Avoid incidental state as much as possible.

it 'publishes the article' do
  article.publish

  # Creating another shared Article test object above would cause this
  # test to break
  expect(Article.count).to eq(2)
end

it 'publishes the article' do
  expect { article.publish }.to change(Article, :count).by(1)
end

Readable matchers

Use readable matchers and double check the available rspec matchers.

lambda { model.save! }.to raise_error Mongoid::Errors::DocumentNotFound

expect { model.save! }.to raise_error Mongoid::Errors::DocumentNotFound

Avoid checking boolean equality directly.

# Class under test:

class Thing
  def awesome?
    true
  end
end

it 'is true' do
  thing = Thing.new
  expect(thing.awesome?).to eq(true)
end

it 'is true' do
  thing = Thing.new
  expect(thing).to be_awesome
end

Use named HTTP status like :no_content over its numeric representation. See a list of supported HTTP status codes
expect(response).to have_http_status(204)
expect(response).to have_http_status(:no_content)

DRY-ing up tests

Avoid using Shared Examples as much as possible. These types of tests do have their place in a few instances but should not be the goto method to write tests.

Extract reusable code into helper methods.

# spec/systems/user_signs_in_spec.rb
RSpec.describe 'User can sign in', type: :system do
  scenario 'logs a user into the application' do
    user = Fabricate(:user)

    visit root_path

    fill_in 'user_session_email',    with: user.email
    fill_in 'user_session_password', with: user.password
    click_button 'Sign in'

    expect(page).to have_content 'Your account'
  end
end

# spec/systems/user_signs_in_spec.rb
RSpec.describe 'User can sign in', type: :system do
  it 'logs a user into the application' do
    sign_in

    expect(page).to have_content 'Your account'
  end
end

# spec/support/authentication_helper.rb
module AuthenticationHelper
  def sign_in
    user = Fabricate(:user)

    visit root_path

    fill_in 'user_session_email',    with: user.email
    fill_in 'user_session_password', with: user.password
    click_button 'Sign in'
  end
end

Test Doubles

Use stubs, mocks and spies to isolate the test to the object under test.
When resorting to mocking and stubbing, only mock against a small, stable, and obvious (or documented) API, so stubs are likely to represent reality after future refactoring.
Avoid stubbing a method to a level where it could give a false-positive test result.

Stubbing HTTP requests

Stub all network requests. Whenever possible, prefer using VCR.

it 'creates a new answer' do
  user = Fabricate(:user)

  # makes a network request
  service = described_class.new(service_params(user.id))

  expect(service.call).to be_a(Api::V1::ForumAnswer)
end

it 'creates a new answer', vcr: 'api/forums/valid-answer' do
  user = Fabricate(:user)

  # network request is stubbed by VCR
  service = described_class.new(service_params(user.id))

  expect(service.call).to be_a(Api::V1::ForumAnswer)
end

When using VCR is not option, we recommend creating a light mock web server using Sinatra.