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Rspec Best Practices

A collection of Rspec testing best practices

Table of Contents

Describe your methods

Keep clear the methods you are describing using "." as prefix for class methods and "#" as prefix for instance methods.

# wrong
describe "the authenticate method for User" do
describe "the save method for User" do

# correct
describe ".authenticate" do
describe "#save" do

Use context

Use context to organize and DRY up code, keep spec descriptions short, and improve test readability.

# wrong
describe User do
  it "should save when name is not empty" do
    User.new(:name => 'Alex').save.should == true
  end

  it "should not save when name is empty" do
    User.new.save.should == false
  end

  it "should not be valid when name is empty" do
    User.new.should_not be_valid
  end

  it "should be valid when name is not empty" do
    User.new(:name => 'Alex').should be_valid
  end
end

# correct
describe User do
  let (:user) { User.new }

  context "when name is empty" do
    it "should not be valid" do
      expect(user.valid?).to be_false
    end

    it "should not save" do
      expect(user.save).to be_false
    end
  end

  context "when name is not empty" do
    let (:user) { User.new(:name => "Alex") }

    it "should be valid" do
      expect(user.valid?).to be_true
    end

    it "should save" do
      expect(user.save).to be_true
    end
  end
end

Only one expectation per example

Each test example should make only one assertion. This helps you on find errors faster and makes your code easier to read and maintain.

# wrong
describe "#fill_gass" do
  it "should have valid arguments" do
    expect { car.fill_gas }.to raise_error(ArgumentError)
    expect { car.fill_gas("foo") }.to_raise_error(TypeError)
  end
end

# correct
describe "#fill_gass" do
  it "should require one argument" do
    expect { car.fill_gas }.to raise_error(ArgumentError)
  end

  it "should require a numeric argument" do
    expect { car.fill_gas("foo") }.to_raise_error(TypeError)
  end
end

Test valid, edge and invalid cases

This is called Boundary value analysis, it’s simple and it will help you to cover the most important cases. Just split-up method’s input or object’s attributes into valid and invalid partitions and test both of them and there boundaries. A method specification might look like that:

describe "#month_in_english(month_id)" do
  context "when valid" do
    it "should return 'January' for 1" # lower boundary
    it "should return 'March' for 3"
    it "should return 'December' for 12" # upper boundary
  end
  context "when invalid" do
    it "should return nil for 0"
    it "should return nil for 13"
  end
end

Use let

When you have to assign a variable to test, instead of using a before each block, use let. It is memoized when used multiple times in one example, but not across examples.

# wrong
describe User, '#locate'
  before(:each) { @user = User.locate }

  it 'should return nil when not found' do
    @user.should be_nil
  end
end

# correct
describe User
  let(:user) { User.locate }

  it 'should have a name' do
    user.name.should_not be_nil
  end
end

DRY

Be sure to apply good code refactoring principles to your tests.

Use before and after hooks:

describe Thing do
  before(:each) do
    @thing = Thing.new
  end

  describe "initialized in before(:each)" do
    it "has 0 widgets" do
      @thing.should have(0).widgets
    end

    it "does not share state across examples" do
      @thing.should have(0).widgets
    end
  end
end

Extract reusable code into helper methods:

# spec/features/user_signs_in_spec.rb
require 'spec_helper'

feature 'User can sign in' do
  scenario 'as a user' do
    sign_in

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

# spec/features/user_signs_out_spec.rb
require 'spec_helper'

feature 'User can sign out' do
  scenario 'as a user' do
    sign_in

    click_link "Logout"

    expect(page).to have_content "Sign up"
  end
end

# spec/support/authentication_helper.rb
module AuthenticationHelper
  def sign_in
    visit root_path

    user = FactoryBot.create(:user)

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

    return user
  end
end

# spec/spec_helper.rb
RSpec.configure do |config|
  config.include AuthenticationHelper, type: :feature
  # ...

Optimize database queries

Large test suites can take a long time to run. Don't load or create more data than necessary.

describe User do
  it 'should return top users in User.top method' do
    @users = (1..3).collect { Factory(:user) }
    top_users = User.top(2).all
    top_users.should have(2).entries
  end
end

class User < ActiveRecord::Base
  named_scope :top, lambda { |*args| { :limit => (args.size > 0 ? args[0] : 10) } }
end

Use factories

Use factory_bot to reduce the verbosity when working with models.

# before
user = User.create( :name => "Genoveffa",
                    :surname => "Piccolina",
                    :city => "Billyville",
                    :birth => "17 Agoust 1982",
                    :active => true)

# after
user = Factory.create(:user)

Choose matchers based on readability

RSpec comes with a lot of useful matchers to help your specs read more like language. When you feel there is a cleaner way … there usually is!

Here are some examples, before and after they are applied:

# before: double negative
object.should_not be_nil
# after: without the double negative
object.should be

# before: 'lambda' is too low level
lambda { model.save! }.should raise_error(ActiveRecord::RecordNotFound)
# after: for a more natural expectation replace 'lambda' and 'should' with 'expect' and 'to'
expect { model.save! }.to raise_error(ActiveRecord::RecordNotFound)

# before: straight comparison
collection.size.should == 4
# after: a higher level size expectation
collection.should have(4).items

Run specific tests

Running your entire test suite over and over again is a waste of time.

Run example or block at specified line:

# in rails
rake spec SPEC=spec/models/demand_spec.rb:30

# not in rails
rspec spec/models/demand_spec.rb:30

Run examples that match a given string:

# in rails
rake spec SPEC=spec/controllers/sessions_controller_spec.rb \
          SPEC_OPTS="-e \"should log in with cookie\""

# not in rails
rspec spec/login_spec.rb -e "should log in with cookie"

In Rails, run only your integration tests:

rake spec:features

Debug Capybara tests with save_and_open_page

Capybara has a save_and_open_page method. As the name implies, it saves the page — complete with styling and images — and opens it in your browser so you can inspect it:

it 'should register successfully' do
  visit registration_page
  save_and_open_page
  fill_in 'username', :with => 'abinoda'
end

Only enable JS in Capybara when necessary

Only enable JS when your tests require it. Enabling JS slows down your test suite.

# only use js => true when your tests depend on it
it 'should register successfully', :js => true do
  visit registration_page
  fill_in 'username', :with => 'abinoda'
end

Unless the pages you are testing require JS, it's best to disable JS after you're done writing the test so that the test suite runs faster.

Consult the logs

When you run any rails application (the webserver, tests or rake tasks), ouput is saved to a log file. There is a log file for each environment: log/development.log, log/test.log, etc.

Take a moment to open up one of these log files in your editor and take a look at its contents. To watch your test log files, use the *nix tool tail:

tail -f log/test.log

Curious what -f means? Check the man page for the tail utility: man tail

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