Use GovukTest to provide headless chrome selenium options

This changes the configuration mechanism for Jasmine selenium runner to
use the approach advised in the gem (as per:
alphagov/content-publisher#2110) and also uses
GovukTest as a means to share the headless chrome configuration.

Gemfile

@@ -19,8 +19,9 @@ gem "uglifier"
 
 group :development, :test do
   gem "govuk_schemas"
+  gem "govuk_test"
   gem "jasmine"
-  gem "jasmine_selenium_runner", require: false
+  gem "jasmine_selenium_runner"
   gem "rubocop-govuk"
   gem "scss_lint-govuk", require: false
 end
@@ -35,7 +36,6 @@ end
 group :test do
   gem "capybara"
   gem "faker"
-  gem "govuk_test"
   gem "minitest-reporters"
   gem "mocha"
   gem "webdrivers"

spec/javascripts/support/jasmine_helper.rb

@@ -1,14 +1,7 @@
-require "jasmine/runners/selenium"
-require "webdrivers/chromedriver"
+require "jasmine_selenium_runner/configure_jasmine"
 
-Jasmine.configure do |config|
-  config.prevent_phantom_js_auto_install = true
-
-  config.runner = lambda { |formatter, jasmine_server_url|
-    options = Selenium::WebDriver::Chrome::Options.new
-    options.headless!
-
-    webdriver = Selenium::WebDriver.for(:chrome, options: options)
-    Jasmine::Runners::Selenium.new(formatter, jasmine_server_url, webdriver, 50)
-  }
+class HeadlessChromeJasmineConfigurer < JasmineSeleniumRunner::ConfigureJasmine
+  def selenium_options
+    { options: GovukTest.headless_chrome_selenium_options }
+  end
 end

spec/javascripts/support/jasmine_selenium_runner.yml

@@ -0,0 +1,2 @@
+browser: chrome
+configuration_class: HeadlessChromeJasmineConfigurer