System testing for Rails application without Capybara, using Puppeteer

Refer this article instead if you can read Japanese sentences.
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Background

Rails introduced "system testing", that makes it easy to configure Capybara: acceptance test framework for Ruby. We may often use it not for "acceptance test" but for just UI testing of the Rails application with React/Vue or other rich JavaScript-powered features.

Capybara DSL is actually a little inaccurate for working with pages with rich JavaScript features.

Capybara has internally polling with interval 10msec for waiting for Elements available and actionable.
https://github.com/teamcapybara/capybara/blob/0468de5a810aae75ab9de20447e246c5c35473f0/lib/capybara/node/base.rb#L91
I don't know this is really the main cause, but we may often face flaky/unstable testcases in using Capybara.

On the other hand, Puppeteer or Playwright have a relyable solution for waiting for Elements: Page#waitForSelector and Page#waitForNavigation. (Playwright has more advanced feature of auto-waiting )

I actually ported the libraries for using them in Rails application.

Playwright for Ruby: https://playwright-ruby-client.vercel.app/
Puppeteer for Ruby: https://github.com/YusukeIwaki/puppeteer-ruby

However the relyable features cannot be used from Capybara DSL. So let's try to configure system tests without Capybara, and using Puppeteer.

What happens if Capybara is absent??

Since Capybara is a huge framework, it would be difficult for some users to imagine what happens without Capybara.

Actually Rails application without Capybara loses the functionalities

Launching test HTTP server on starting tests
Capybara::DSL
- Using visit or other methods raises NoMethodError instead of NotImplementedError
- System spec (on RSpec) or SystemTestCase (on MiniTest), which depends on Capybara::DSL

However rspec-rails still provides features like

Attaching type: :feature type: :system to example.metadata
Defining feature background scenario methods for feature spec

So actually all we have to prepare is

Launching test HTTP server
Performing automation with browsers
- This will be satisfied by Puppeteer

Launching test HTTP server without Capybara

Capybara is really kind that

finds available port
allows to configure host
allows to launch Webrick and Puma

However let's forget them at this moment, and assume that we only have to launch Puma with the baseURL http://127.0.0.1:3000

With referring the logics of Capybara preparing server and launching Puma server, then we can easily find the minimum configuration for launching test server like below:

RSpec.configure do |config|
  config.before(:suite) do
    # launching Rails server for system testing
    require 'rack/builder'
    testapp = Rack::Builder.app(Rails.application) do
      map '/__ping' do # debugging endpoint for heartbeat
        run ->(env) { [200, { 'Content-Type' => 'text/plain' }, ['OK']] }
      end
    end

    require 'rack/handler/puma'
    server_thread = Thread.new do
      Rack::Handler::Puma.run(testapp,
        Host: '127.0.0.1',
        Port: 3000,
        Threads: '0:4',
        workers: 0,
        daemonize: false,
      )
    end

    # Waiting for Rails server is ready, using Net::HTTP
    require 'net/http'
    require 'timeout'
    Timeout.timeout(3) do
      loop do
        puts Net::HTTP.get(URI("http://127.0.0.1:3000/__ping"))
        break
      rescue Errno::EADDRNOTAVAIL
        sleep 1
      rescue Errno::ECONNREFUSED
        sleep 0.1
      end
    end
  end

  # Configure puppeteer-ruby for automation
  config.around(type: :feature) do |example|
    Puppeteer.launch(channel: :chrome, headless: false) do |browser|
      @server_base_url = 'http://127.0.0.1:3000'
      @puppeteer_page = browser.new_page
      example.run
    end
  end
end

By putting this configuration into spec/support/integration_test_helper.rb or another place you prefer, now we can enjoy system testing with Puppeteer like below!!

As is already described, we cannot use system spec. Use feature spec (provided by rspec-rails) instead.

require 'rails_helper'

describe 'example' do
  let(:base_url) { @server_base_url }
  let(:page) { @puppeteer_page }

  let(:user) { FactoryBot.create(:user) }

  it 'can browse' do
    page.goto("#{base_url}/tests/#{user.id}")
    page.wait_for_selector('input', visible: true)
    page.type_text('input', 'hoge')
    page.keyboard.press('Enter')

    text = page.eval_on_selector('#content', 'el => el.textContent')
    expect(text).to include('hoge')
    expect(text).to include(user.name)
  end
end

A little refactoring for production use

The logic of launching test server, introduced in the previous section, is really straightforward. However most users would hesitate to copy/paste it into your own products because it's too dirty :(

No worry, here is a better code with more relyable Rack::Server.start to launch HTTP server, which is actually used in the implementation of rackup command

class RackTestServer
  def initialize(app:, **options)
    @options = options

    @options[:Host] ||= '127.0.0.1'
    @options[:Port] ||= 3000

    require 'rack/builder'
    @options[:app] = Rack::Builder.app(app) do
      map '/__ping' do
        run ->(env) { [200, { 'Content-Type' => 'text/plain' }, ['OK']] }
      end
    end
  end

  def base_url
    "http://#{@options[:Host]}:#{@options[:Port]}"
  end

  def start
    require 'rack/server'
    Rack::Server.start(**@options)
  end

  def ready?
    require 'net/http'
    begin
      Net::HTTP.get(URI("#{base_url}/__ping"))
      true
    rescue Errno::EADDRNOTAVAIL
      false
    rescue Errno::ECONNREFUSED
      false
    end
  end

  def wait_for_ready(timeout: 3)
    require 'timeout'
    Timeout.timeout(3) do
      sleep 0.1 until ready?
    end
  end
end

With this test server, the RSpec configuration file can be much shorter and simplified :)

RSpec.configure do |config|
  config.before(:suite) do
    # Launch Rails application
    test_server = RackTestServer.new(
      # options for Rack::Server
      # https://github.com/rack/rack/blob/2.2.3/lib/rack/server.rb#L173
      app: Rails.application,
      server: :puma,
      Host: '127.0.0.1',
      Port: 3000,
      daemonize: false,

      # options for Rack::Handler::Puma
      # https://github.com/puma/puma/blob/v5.4.0/lib/rack/handler/puma.rb#L84
      Threads: '0:4',
      workers: 0,
    )

    Thread.new { test_server.start }
    test_server.wait_for_ready
  end

  # Configure puppeteer-ruby for automation
  config.around(type: :feature) do |example|
    Puppeteer.launch(channel: :chrome, headless: false) do |browser|
      @server_base_url = 'http://127.0.0.1:3000'
      @puppeteer_page = browser.new_page
      example.run
    end
  end
end

Now, you can now get rid of Capybara from your app if you just want to launch HTTP server for testing :)

You can also use rack-test_server Gem instead of defining your own RackTestServer.

Blog

System testing for Rails application without Capybara, using Puppeteer

Yusuke Iwaki

Background

What happens if Capybara is absent??

Launching test HTTP server without Capybara

A little refactoring for production use

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