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RSpec ⛑

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To test Rails applications, the team prefers using RSpec over MiniTest but restrains itself to its core features and uses 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

Types

  • Use Request tests over Controller tests.

    Controller tests are being deprecated. As the Rails community is migrating to use Request tests instead.

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

  • Avoid unnecessary database interactions.

    it 'returns the user\'s full name' do
  # Unnecessary information in database
  user = Fabricate(:user, first_name: 'John', last_name: 'Terry')

  expect(user.full_name).to eq 'John Terry'
end

    it 'returns the user\'s full name' do
  # Just build the user object
  user = Fabricate.build(:user, first_name: 'John', last_name: 'Terry')

  expect(user.full_name).to eq 'John Terry'
end

Assertion

Expectation(s) per test

  • For unit tests — i.e. running in isolation, 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) }

  • Integration tests — i.e., mainly request, service, and some model tests may suffer a performance hit when the setup is complex. Therefore, each integration test can contain multiple assertions.

    RSpec.describe SendInvitationService, type: :service do
  describe '#call' do
    context 'given valid params' do
      it 'returns true' do
        company = Fabricate(:company)
        user = Fabricate(:user, company: company)
        invitation = Fabricate(:invitation, status: :draft)

        service = described_class.new(invitation: invitation, user: user)

        result = service.call

        expect(result).to be(true)
      end

      it 'sends the invitations' do
        company = Fabricate(:company)
        user = Fabricate(:user, company: company)
        invitation = Fabricate(:invitation, status: :draft)

        service = described_class.new(invitation: invitation, user: user)

        result = service.call

        expect(invitation.status).to eq(:sent)
      end
    end
  end
end

    RSpec.describe SendInvitationService, type: :service do
  describe '#call' do
    context 'given valid params' do
      it 'returns true and sends the invitations' do
        company = Fabricate(:company)
        user = Fabricate(:user, company: company)
        invitation = Fabricate(:invitation, status: :draft)

        service = described_class.new(invitation: invitation, user: user)

        result = service.call

        expect(result).to be(true)
        expect(invitation.status).to eq(:sent)
      end
    end
  end
end

  • For system tests — i.e. UI tests, tests with multiple expectations are the norm: once a scenario has run, a system test often needs to assert the presence of several UI elements and their values.

    describe 'Delete an event', type: :system do
  context 'given the delete button is clicked' do
    it 'displays the confirmation message within the delete modal' do
      [...]
    end

    it 'displays the cancel button within the delete modal' do
      [...]
    end

    it 'displays the delete button within the delete modal' do
      [...]
    end
  end
end

    describe 'Delete an event', type: :system do
  context 'given the delete button is clicked' do
    it 'displays the delete modal' do
      user = Fabricate(:user)
      event = Fabricate(:event)

      login_as user
      visit edit_event_path(id: event)

      click_link I18n.t('helpers.submit.delete', resource: Event.model_name)

      within '.modal[data-testid="modal_delete"]' do
        expect(page).to have_content(I18n.t('activerecord.messages.destroy.confirm.default', resource: event.name))
        expect(page).to have_button(I18n.t('activerecord.actions.cancel'))
        expect(page).to have_button(I18n.t('helpers.submit.delete'))
      end
    end
  end
end

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

Creating a light mock web server using Sinatra is recommended when using VCR is not an option.