Testing Rails app with Docker containers

docker-compose.yml

# ./docker-compose.yml
version: "3"
services:
  app:
    build: .
    env_file:
      - .env
    ports:
      - 3000:3000 # app
      - 35729:35729 # live reload
    links:
      - postgres
    volumes:
      - app-sync:/app:nocopy

  test:
    build: .
    env_file:
      - .env.test
    ports:
      - 3005:3005 # Capybara listens here
    links:
      - postgres
      - selenium
    volumes:
      - app-sync:/app:nocopy
    command: bin/spring server
    environment:
      TEST_APP_HOST: test
      TEST_APP_PORT: 3005
      SELENIUM_HOST: selenium
      RAILS_ENV: test
    networks:
      default:
        aliases:
          - test

  postgres:
    image: postgres:9.4
    ports:
      - 5432
    volumes:
      - './postgres-data:/var/lib/postgresql/data'

  selenium:
    image: selenium/standalone-chrome-debug
    ports:
      - 5900:5900

volumes:
  app-sync:
    external: true

feature_helper.rb

# ./spec/features/feature_helper.rb
# ...
SELENIUM_HOST = ENV['SELENIUM_HOST']
TEST_APP_HOST = ENV['TEST_APP_HOST']
TEST_APP_PORT = ENV['TEST_APP_PORT']

Capybara.register_driver :selenium_remote do |app|
  Capybara::Selenium::Driver.new(
    app,
    browser: :remote,
    url: "http://#{SELENIUM_HOST}:4444/wd/hub",
    desired_capabilities: Selenium::WebDriver::Remote::Capabilities.chrome
  )
end

Capybara.javascript_driver = :selenium_remote
Capybara.server_port = TEST_APP_PORT
Capybara.server_host = '0.0.0.0'
Capybara.app_host = "http://#{TEST_APP_HOST}:#{TEST_APP_PORT}"
# ...