System Testing

System tests let you test applications in the browser. Because system tests use a real browser experience, you can test all of your JavaScript easily from your test suite.

To create a system test in your application, extend your test class from ApplicationSystemTestCase. System tests use Capybara as a base and allow you to configure the settings through your application_system_test_case.rb file that is generated with a new application or scaffold.

Here is an example system test:

require "application_system_test_case"

class Users::CreateTest < ApplicationSystemTestCase
  test "adding a new user" do
    visit users_path
    click_on 'New User'

    fill_in 'Name', with: 'Arya'
    click_on 'Create User'

    assert_text 'Arya'
  end
end

When generating an application or scaffold, an application_system_test_case.rb file will also be generated containing the base class for system testing. This is where you can change the driver, add Capybara settings, and other configuration for your system tests.

require "test_helper"

class ApplicationSystemTestCase < ActionDispatch::SystemTestCase
  driven_by :selenium, using: :chrome, screen_size: [1400, 1400]
end

By default, ActionDispatch::SystemTestCase is driven by the Selenium driver, with the Chrome browser, and a browser size of 1400x1400.

Changing the driver configuration options is easy. Let's say you want to use the Firefox browser instead of Chrome. In your application_system_test_case.rb file add the following:

require "test_helper"

class ApplicationSystemTestCase < ActionDispatch::SystemTestCase
  driven_by :selenium, using: :firefox
end

driven_by has a required argument for the driver name. The keyword arguments are :using for the browser and :screen_size to change the size of the browser screen. These two options are not applicable for headless drivers and will be silently ignored if passed.

Headless browsers such as headless Chrome and headless Firefox are also supported. You can use these browsers by setting the :using argument to :headless_chrome or :headless_firefox.

To use a headless driver, like Poltergeist, update your Gemfile to use Poltergeist instead of Selenium and then declare the driver name in the application_system_test_case.rb file. In this case, you would leave out the :using option because the driver is headless, but you can still use :screen_size to change the size of the browser screen, also you can use :options to pass options supported by the driver. Please refer to your driver documentation to learn about supported options.

require "test_helper"
require "capybara/poltergeist"

class ApplicationSystemTestCase < ActionDispatch::SystemTestCase
  driven_by :poltergeist, screen_size: [1400, 1400], options:
    { js_errors: true }
end

Some drivers require browser capabilities to be passed as a block instead of through the options hash.

As an example, if you want to add mobile emulation on chrome, you'll have to create an instance of selenium's Chrome::Options object and add capabilities with a block.

The block will be passed an instance of <Driver>::Options where you can define the capabilities you want. Please refer to your driver documentation to learn about supported options.

class ApplicationSystemTestCase < ActionDispatch::SystemTestCase
  driven_by :selenium, using: :chrome, screen_size: [1024, 768] do |driver_option|
    driver_option.add_emulation(device_name: 'iPhone 6')
    driver_option.add_extension('path/to/chrome_extension.crx')
  end
end

Because ActionDispatch::SystemTestCase is a shim between Capybara and Rails, any driver that is supported by Capybara is supported by system tests as long as you include the required gems and files.