Apparition - A Chrome driver for Capybara

Apparition is a driver for Capybara. It allows you to run your Capybara tests in the Chrome browser via CDP (no selenium or chromedriver needed) in a headless or headed configuration. It started as a fork of Poltergeist and attempts to maintain as much compatibility with the Poltergeist API as possible. Implementing the capybara-webkit specific driver methods has also begun.

Questions should be posted on Stack Overflow, using the 'capybara' tag and mentioning you are using the apparition driver.

Bug reports should be posted on GitHub (and be sure to read the bug reporting guidance below).

Add either

gem 'apparition'

or

gem 'apparition', github: 'twalpole/apparition'

to your Gemfile and run bundle install.

In your test setup add:

require 'capybara/apparition'
Capybara.javascript_driver = :apparition

If you were previously using the :rack_test driver, be aware that your app will now run in a separate thread and this can have consequences for transactional tests. See the Capybara README for more detail.

Apparition supports all Capybara features, and the following extended features:

• page.status_code
• page.response_headers
• page.driver.render_base64(format, options)
• page.driver.scroll_to(left, top)
• page.driver.basic_authorize(user, password)
• page.driver.set_proxy(host, port, type, user, password, bypass: [bypass list passed to chrome])
• cookie handling
• extra headers

There are some additional features:

You can grab screenshots of the page at any point by calling save_screenshot('/path/to/file.png').

By default, only the viewport will be rendered (the part of the page that is in view). To render the entire page, use save_screenshot('/path/to/file.png', full: true).

You also have an ability to render selected element. Pass option selector with any valid CSS element selector to make a screenshot bounded by that element save_screenshot('/path/to/file.png', selector: '#id').

If the desired image format is not identifiable from the filename passed you can also pass in a format: option with accepable values being :png or :jpeg

If, for some reason, you need a base64 encoded screenshot you can simply call render_base64 which will return your encoded image. Additional options are the same as for save_screenshot.

Sometimes its desirable to click a very specific area of the screen. You can accomplish this with page.driver.click(x, y), where x and y are the screen coordinates.

If you use the :inspector => true option (see below), remote debugging will be enabled.

When this option is enabled, you can insert page.driver.debug into your tests to pause the test and launch a browser which gives you the WebKit inspector to view your test run with.

You can register this debugger driver with a different name and set it as the current javascript driver. By example, in your helper file:

Capybara.register_driver :apparition_debug do |app|
  Capybara::Apparition::Driver.new(app, :inspector => true)
end
# Capybara.javascript_driver = :apparition
Capybara.javascript_driver = :apparition_debug

Read more here

You can manipulate HTTP request headers with these methods:

page.driver.headers # => {}
page.driver.headers = { "User-Agent" => "Apparition" }
page.driver.add_headers("Referer" => "https://example.com")
page.driver.headers # => { "User-Agent" => "Apparition", "Referer" => "https://example.com" }

Notice that headers= will overwrite already set headers. You should use add_headers if you want to add a few more. These headers will apply to all subsequent HTTP requests (including requests for assets, AJAX, etc). They will be automatically cleared at the end of the test. You have ability to set headers only for the initial request:

page.driver.headers = { "User-Agent" => "Apparition" }
page.driver.add_header("Referer", "http://example.com", permanent: false)
page.driver.headers # => { "User-Agent" => "Apparition", "Referer" => "http://example.com" }
visit(login_path)
page.driver.headers # => { "User-Agent" => "Apparition" }

This way your temporary headers will be sent only for the initial request, and related 30x redirects. All subsequent request will only contain your permanent headers. If the temporary headers should not be sent on related 30x redirects, specify permanent: :no_redirect.

You can inspect the network traffic (i.e. what resources have been loaded) on the current page by calling page.driver.network_traffic. This returns an array of request objects. A request object has a response_parts method containing data about the response chunks.

You can inspect requests that were blocked by a whitelist or blacklist by calling page.driver.network_traffic(:blocked). This returns an array of request objects. The response_parts portion of these requests will always be empty.

Please note that network traffic is not cleared when you visit new page. You can manually clear the network traffic by calling page.driver.clear_network_traffic or page.driver.reset

The following methods are used to inspect and manipulate cookies:

• page.driver.cookies - a hash of cookies accessible to the current page. The keys are cookie names. The values are Cookie objects, with the following methods: name, value, domain, path, secure?, httponly?, samesite, expires.
• page.driver.set_cookie(name, value, options = {}) - set a cookie. The options hash can take the following keys: :domain, :path, :secure, :httponly, :samesite, :expires. :expires should be a Time object.
• page.driver.remove_cookie(name) - remove a cookie
• page.driver.clear_cookies - clear all cookies

You can customize the way that Capybara sets up Apparition via the following code in your test setup:

Capybara.register_driver :apparition do |app|
  Capybara::Apparition::Driver.new(app, options)
end

options is a hash of options. The following options are supported:

• :headless (Boolean) - When false, run the browser visibly
• :remote (Boolean) - When true, connect to remote browser instead of starting locally (see [below](#Remote Chrome Driver))
• :debug (Boolean) - When true, debug output is logged to STDERR.
• :logger (Ruby logger object or any object responding to puts) - When present, debug output is written to this object
• :browser_logger (IO object) - This is where your console.log statements will show up. Default: STDOUT
• :timeout (Numeric) - The number of seconds we'll wait for a response when communicating with Chrome. Default is 30.
• :inspector (Boolean, String) - See 'Remote Debugging', above.
• :js_errors (Boolean) - When false, JavaScript errors do not get re-raised in Ruby.
• :window_size (Array) - The dimensions of the browser window in which to test, expressed as a 2-element array, e.g. [1024, 768]. Default: [1024, 768]
• :screen_size (Array) - The dimensions the window size will be set to when Window#maximize is called in headless mode. Expressed as a 2-element array, e.g. [1600, 1200]. Default: [1366, 768]
• :extensions (Array) - An array of JS files to be preloaded into the browser. Useful for faking or mocking APIs.
• :url_blacklist (Array) - Default session url blacklist - expressed as an array of strings to match against requested URLs.
• :url_whitelist (Array) - Default session url whitelist - expressed as an array of strings to match against requested URLs.
• :ignore_https_errors (Boolean) - Ignore certificate errors when connecting to https URLs.
• :browser_options (Hash) - Extra command line options to pass to Chrome when starting
• :skip_image_loading (Boolean) - Don't load images

Apparition can connect to already running instance of chrome. Remote mode is useful when running tests in CI and chrome is available as separate docker container.

In order to use remote browser - set up apparition in the following way:

Capybara.register_driver :apparition do |app|
  browser_options = { 'remote-debugging-address' => '127.0.0.1', 'remote-debugging-port' => 9999 }
  Capybara::Apparition::Driver.new(app, remote: true, browser_options: browser_options)
end

In order to use Apparition on a Linux server, you need to install the chrome binary and set certain :browser_options.

wget https://dl.google.com/linux/direct/google-chrome-stable_current_amd64.deb
sudo apt install -f ./google-chrome-stable_current_amd64.deb

Capybara.register_driver :apparition do |app|
  Capybara::Apparition::Driver.new(app, browser_options: { 'no-sandbox' => nil, 'disable-web-security' => nil, 'disable-features' => 'VizDisplayCompositor' })
end

This will enable your scripts to visit remote websites.

Apparition supports URL blacklisting, which allows you to prevent scripts from running on designated domains:

page.driver.browser.url_blacklist = ['http://www.example.com']

and also URL whitelisting, which allows scripts to only run on designated domains:

page.driver.browser.url_whitelist = ['http://www.example.com']

If you are experiencing slower run times, consider creating a URL whitelist of domains that are essential or a blacklist of domains that are not essential, such as ad networks or analytics, to your testing environment.

Desktop Chrome often won't let you set the window width narrower than 500px without also enabling mobile emulation, even when Chrome appears to accept the width.

To test with mobile widths, it's necessary to enable mobile emulation via CDP with all the required parameters.

nexus_5_metrics = {
  mobile: true,
  screenWidth: 412,
  screenHeight: 660,
  width: 412,
  height: 660,
  positionX: 0,
  positionY: 0,

  scale: 1,
  deviceScaleFactor: 2.625,
  screenOrientation: {
    angle: 0,
    type: "portraitPrimary",
  },
}

page.driver.browser.current_page.command(
  "Emulation.setDeviceMetricsOverride",
  **nexus_5_metrics,
)

page.driver.browser.current_page.command(
  "Emulation.setTouchEmulationEnabled",
  { enabled: true },
)

These settings put Chrome in mobile emulation mode in the same fashion as enabling the emulation mode from the developer tools.

Sometimes tests pass and fail sporadically. This is often because there is some problem synchronising events properly. It's often straightforward to verify this by adding sleep statements into your test to allow sufficient time for the page to settle.

If you have these types of problems, read through the Capybara documentation on asynchronous JavaScript which explains the tools that Capybara provides for dealing with this.

If you can provide specific steps to reproduce your problem, or have specific information that might help track down the problem, then please file a bug on Github.

Include as much information as possible. For example:

• Specific steps to reproduce where possible (failing tests are even better)
• The output obtained from running Apparition with :debug turned on or ENV['DEBUG'] set
• Screenshots
• Stack traces if there are any Ruby on JavaScript exceptions generated
• The Apparition, Capybara, and Chrome version numbers used
• The operating system name and version used

Version history and a list of next-release features and fixes can be found in the changelog.

Copyright (c) 2019 Thomas Walpole

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.