Use Selenium with Docker and RSpec

October 25, 2023

This is a technical post, meant to share knowledge from my adventures on a work project yesterday. The combination of using an official Docker selenium Chrome image and Rails system tests is not well documented if you use RSpec. My contribution is below the fold.

Why Do This

If you run a complex application then orchestrating its components with Docker and Docker Compose can simplify development. Instead of having to configure a bunch of local services, you can drop a .env file in your app repo and then try docker compose up. If you then also deploy with Docker, you eliminate the issue of differences between your development and production environments when you need to debug something.

How to Configure Docker

Just add something like the following to your docker-compose.yml:

    image: selenium/standalone-chrome:latest
    container_name: consus_lite_selenium
      - 4444:4444
      - consusnet

Make sure the network uses the same container as your Rails application.

Your Gemfile

Make sure to include:

gem 'selenium-webdriver

in your test group.

How to Configure RSPec

In spec/spec_helper.rb:

require 'capybara/rspec'
# Configurtion for Capybara System Tests in Docker Remote
Capybara.server_host = ""
Capybara.app_host = "http://#{IPSocket.getaddress(Socket.gethostname)}"

Then for your tests that require Selenium (put in a before block or update Capybara’s default configuration):

driven_by(:selenium, using: :headless_chrome, options: { browser: :remote, url: 'http://selenium:4444' })
WebMock.disable_net_connect!(allow_localhost: true, allow: 'selenium')

In the above block you can interchange :headless_chrome with your selenium browser of choice, provided you are using the corresponding image. Using :chrome instead of :headless_chrome will let you look at the browser execution in the container’s web interface. You will need to replace selenium in the url and allow keyword arguments to use the name of the container you used in docker-compose.yml. You can skip the Webmock statement if you do not use WebMock.

Be Smart: Do Not Be Tricked by ChatGPT

When I asked ChatGPT how to do this it told me to try:

driven_by :selenium, using: :remote, url: 'http://remote-server-ip:4444/wd/hub', desired_capabilities: :chrome

The above throws a somewhat challenging to debug error. The above approach is potentially influenced by the Official Selenium Documentation. However, you’ll note there is a difference between the Selenium gem being called directly and calling it through Rails.

As I have been experimenting with ChatGPT to accelerate my development work, I have found it to be a net negative.

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This work by Matt Zagaja is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.