Add a new integration test helper

Add an integration test helper for use in integration tests for pages
 that have been transitioned to the GOV.UK Design System.

Has a minimal implementation for now, which is copied from the legacy
 integration test helper.

test/integration/downtime_integration_test.rb

@@ -1,6 +1,6 @@
-require "legacy_integration_test_helper"
+require "integration_test_helper"
 
-class DowntimeIntegrationTest < LegacyJavascriptIntegrationTest
+class DowntimeIntegrationTest < JavascriptIntegrationTest
   setup do
     setup_users
 

test/integration/downtime_with_invalid_dates_test.rb

@@ -1,6 +1,6 @@
-require "legacy_integration_test_helper"
+require "integration_test_helper"
 
-class DowntimeWithInvalidDates < LegacyPublisherIntegrationTest
+class DowntimeWithInvalidDates < PublisherIntegrationTest
   setup do
     setup_users
 

test/integration_test_helper.rb

@@ -0,0 +1,62 @@
+require "test_helper"
+require "capybara/rails"
+require "capybara-select-2"
+require "support/govuk_test"
+
+class PublisherIntegrationTest < ActionDispatch::IntegrationTest
+  include Capybara::DSL
+  include CapybaraSelect2
+  include CapybaraSelect2::Helpers
+  include Warden::Test::Helpers
+
+  teardown do
+    Capybara.reset_sessions! # Forget the (simulated) browser state
+    Capybara.use_default_driver # Revert Capybara.current_driver to Capybara.default_driver
+    GDS::SSO.test_user = nil
+  end
+
+  def setup_users
+    # This may not be the right way to do things. We rely on the gds-sso
+    # having a strategy that uses the first user. We probably want some
+    # tests that cover the oauth interaction properly
+    @author = FactoryBot.create(:user, :govuk_editor, name: "Author", email: "[email protected]")
+    @reviewer = FactoryBot.create(:user, :govuk_editor, name: "Reviewer", email: "[email protected]")
+  end
+
+  def login_as(user)
+    GDS::SSO.test_user = user
+    super(user)
+  end
+end
+
+class JavascriptIntegrationTest < PublisherIntegrationTest
+  setup do
+    Capybara.current_driver = Capybara.javascript_driver
+  end
+
+  # Get a single user by their name. If the user doesn't exist, return nil.
+  def get_user(name)
+    User.where(name:).first
+  end
+
+  # Set the given user to be the current user
+  # Accepts either a User object or a user's name
+  def login_as(user)
+    unless user.is_a?(User)
+      user = get_user(user)
+    end
+    clear_cookies
+    GDS::SSO.test_user = user
+  end
+
+  def clear_cookies
+    browser = Capybara.current_session.driver.browser
+    if browser.respond_to?(:clear_cookies)
+      # Rack::MockSession
+      browser.clear_cookies
+    elsif browser.respond_to?(:manage) && browser.manage.respond_to?(:delete_all_cookies)
+      # Selenium::WebDriver
+      browser.manage.delete_all_cookies
+    end
+  end
+end