Use AB Testing Gem

Gemfile

@@ -20,6 +20,7 @@ gem 'unicorn', '4.8'
 gem 'rails-i18n', '>= 4.0.4'
 gem 'rails_translation_manager', '~> 0.0.2'
 gem 'rails-controller-testing', '~> 0.1'
+gem 'govuk_ab_testing', '0.1.0'
 
 if ENV['API_DEV']
   gem 'gds-api-adapters', path: '../gds-api-adapters'

Gemfile.lock

@@ -83,6 +83,7 @@ GEM
     govuk-lint (1.2.0)
       rubocop (~> 0.39.0)
       scss_lint
+    govuk_ab_testing (0.1.0)
     govuk_frontend_toolkit (5.1.0)
       rails (>= 3.1.0)
       sass (>= 3.2.0)
@@ -253,6 +254,7 @@ DEPENDENCIES
   gds-api-adapters (= 39.1.0)
   govuk-content-schema-test-helpers (= 1.1.0)
   govuk-lint
+  govuk_ab_testing (= 0.1.0)
   govuk_frontend_toolkit (= 5.1.0)
   govuk_navigation_helpers (~> 2.1.0)
   jasmine-rails (~> 0.13.0)

app/controllers/content_items_controller.rb

@@ -1,11 +1,13 @@
 require 'gds_api/content_store'
 
 class ContentItemsController < ApplicationController
-  include ABTestable
+  include EducationNavigationABTestable
 
   rescue_from GdsApi::HTTPForbidden, with: :error_403
   rescue_from GdsApi::HTTPNotFound, with: :error_notfound
 
+  attr_accessor :content_item
+
   def show
     load_content_item
     set_expiry
@@ -15,11 +17,6 @@ def show
     end
   end
 
-  # Visible for testing
-  def should_present_new_navigation_view?
-    (education_navigation_ab_testing_group == "B") && new_navigation_enabled? && content_is_tagged_to_a_taxon?
-  end
-
 private
 
   def load_content_item
@@ -74,12 +71,4 @@ def error_notfound
   def set_page_variant
     request.variant = :new_navigation if should_present_new_navigation_view?
   end
-
-  def new_navigation_enabled?
-    ENV['ENABLE_NEW_NAVIGATION'] == 'yes'
-  end
-
-  def content_is_tagged_to_a_taxon?
-    @content_item.taxons.any?
-  end
 end

app/presenters/content_item_presenter.rb

@@ -29,14 +29,6 @@ def content_id
     content_item.parsed_content["content_id"]
   end
 
-  def taxons
-    if content_item["links"].include?("taxons")
-      content_item["links"]["taxons"]
-    else
-      []
-    end
-  end
-
   def breadcrumbs
     @nav_helper.breadcrumbs[:breadcrumbs]
   end

app/presenters/education_navigation_ab_testable.rb

@@ -0,0 +1,30 @@
+module EducationNavigationABTestable
+  def education_navigation_ab_test
+    @ab_test ||= GovukAbTesting::AbTest.new("educationnavigation")
+  end
+
+  def should_present_new_navigation_view?
+    education_navigation_variant.variant_b? && new_navigation_enabled? && content_is_tagged_to_a_taxon?
+  end
+
+  def education_navigation_variant
+    @education_navigation_variant ||= education_navigation_ab_test.requested_variant request
+  end
+
+  def new_navigation_enabled?
+    ENV['ENABLE_NEW_NAVIGATION'] == 'yes'
+  end
+
+  def content_is_tagged_to_a_taxon?
+    content_item.content_item.dig("links", "taxons").present?
+  end
+
+  def set_education_navigation_response_header
+    education_navigation_variant.configure_response response
+  end
+
+  def self.included(base)
+    base.helper_method :education_navigation_variant
+    base.after_filter :set_education_navigation_response_header
+  end
+end

test/controllers/content_items_controller_test.rb

@@ -3,6 +3,14 @@
 class ContentItemsControllerTest < ActionController::TestCase
   include GdsApi::TestHelpers::ContentStore
 
+  setup do
+    ENV['ENABLE_NEW_NAVIGATION'] = 'yes'
+  end
+
+  teardown do
+    ENV['ENABLE_NEW_NAVIGATION'] = nil
+  end
+
   test "routing handles translated content paths" do
     translated_path = 'government/case-studies/allez.fr'
 
@@ -76,8 +84,6 @@ class ContentItemsControllerTest < ActionController::TestCase
   end
 
   test "honours Education Navigation AB Testing cookie" do
-    ENV['ENABLE_NEW_NAVIGATION'] = 'yes'
-
     content_item = content_store_has_schema_example('case_study', 'case_study')
     path = 'government/abtest/easy-as-1-2'
     content_item['base_path'] = "/#{path}"
@@ -97,8 +103,6 @@ class ContentItemsControllerTest < ActionController::TestCase
   end
 
   test "does not show new navigation when no taxons tagged to content" do
-    ENV['ENABLE_NEW_NAVIGATION'] = 'yes'
-
     content_item = content_store_has_schema_example('case_study', 'case_study')
     path = 'government/abtest/easy-as-1-2'
     content_item['base_path'] = "/#{path}"