Add content navigation multivariate test

Start with 4 variants:
original, no nav, taxonomy nav, mainstream nav

* Follow “concern” pattern setup in #513 for task list AB test
* Only content with the document types listed are part of the test
* The content must also be tagged to a taxon
* Use a “universal_navigation” variant for all multivariate tests
except original – they are largely the same, significant differences
with original shouldn’t be repeated

app/controllers/concerns/content_navigation_ab_testable.rb

@@ -0,0 +1,86 @@
+module ContentNavigationABTestable
+  CONTENT_NAVIGATION_DIMENSION = 67
+  CONTENT_NAVIGATION_ORIGINAL = "Original".freeze
+  CONTENT_NAVIGATION_UNIVERSAL_NO_NAVIGATION = "UniversalNoNav".freeze
+  CONTENT_NAVIGATION_UNIVERSAL_MAINSTREAM_NAVIGATION = "UniversalMainstreamNav".freeze
+  CONTENT_NAVIGATION_UNIVERSAL_TAXON_NAVIGATION = "UniversalTaxonNav".freeze
+
+  CONTENT_NAVIGATION_ALLOWED_VARIANTS = [
+    CONTENT_NAVIGATION_ORIGINAL,
+    CONTENT_NAVIGATION_UNIVERSAL_NO_NAVIGATION,
+    CONTENT_NAVIGATION_UNIVERSAL_MAINSTREAM_NAVIGATION,
+    CONTENT_NAVIGATION_UNIVERSAL_TAXON_NAVIGATION
+  ].freeze
+
+  GUIDANCE_DOCUMENT_TYPES = %w(
+    answer
+    guide
+    detailed_guide
+    statutory_guidance
+  ).freeze
+
+  def self.included(base)
+    base.helper_method(
+      :content_navigation_variant,
+      :content_navigation_ab_test_applies?,
+      :content_navigation_test_original_variant?,
+      :universal_navigation_without_nav?,
+      :universal_navigation_with_taxon_nav?,
+      :universal_navigation_with_mainstream_nav?
+    )
+
+    base.after_action :set_content_navigation_response_header
+  end
+
+  def content_navigation_ab_test
+    @content_navigation_ab_test ||=
+      GovukAbTesting::AbTest.new(
+        "ContentNavigation",
+        dimension: CONTENT_NAVIGATION_DIMENSION,
+        allowed_variants: CONTENT_NAVIGATION_ALLOWED_VARIANTS
+      )
+  end
+
+  # Universal navigation:
+  # https://gov-uk.atlassian.net/wiki/spaces/GFED/pages/186351726/Sprint+1+designs
+  #
+  # Universal navigation must only be shown when:
+  # * in the multivariate test
+  # * not showing the original variant
+  def should_present_universal_navigation?
+    content_navigation_ab_test_applies? && !content_navigation_test_original_variant?
+  end
+
+  def content_navigation_ab_test_applies?
+    @content_item.tagged_to_a_taxon? && content_document_type_is_guidance?
+  end
+
+  def content_document_type_is_guidance?
+    GUIDANCE_DOCUMENT_TYPES.include? @content_item.document_type
+  end
+
+  def content_navigation_test_original_variant?
+    content_navigation_variant.variant?(CONTENT_NAVIGATION_ORIGINAL)
+  end
+
+  def universal_navigation_without_nav?
+    content_navigation_variant.variant?(CONTENT_NAVIGATION_UNIVERSAL_NO_NAVIGATION)
+  end
+
+  def universal_navigation_with_taxon_nav?
+    content_navigation_variant.variant?(CONTENT_NAVIGATION_UNIVERSAL_TAXON_NAVIGATION)
+  end
+
+  def universal_navigation_with_mainstream_nav?
+    content_navigation_variant.variant?(CONTENT_NAVIGATION_UNIVERSAL_MAINSTREAM_NAVIGATION)
+  end
+
+  def content_navigation_variant
+    @content_navigation_variant ||=
+      content_navigation_ab_test.requested_variant(request.headers)
+  end
+
+  def set_content_navigation_response_header
+    content_navigation_variant.configure_response(response) if content_navigation_ab_test_applies?
+  end
+end

app/controllers/content_items_controller.rb

@@ -2,6 +2,7 @@ class ContentItemsController < ApplicationController
   class SpecialRouteReturned < StandardError; end
 
   include TasklistABTestable
+  include ContentNavigationABTestable
 
   rescue_from GdsApi::HTTPForbidden, with: :error_403
   rescue_from GdsApi::HTTPNotFound, with: :error_notfound
@@ -14,8 +15,9 @@ class SpecialRouteReturned < StandardError; end
 
   def show
     load_content_item
-    set_up_navigation
     setup_tasklist_ab_testing
+    setup_content_navigation_ab_testing
+    set_up_navigation
     set_expiry
     set_access_control_allow_origin_header if request.format.atom?
     set_guide_draft_access_token if @content_item.is_a?(GuidePresenter)
@@ -89,17 +91,20 @@ def set_expiry
   end
 
   def set_up_navigation
-    @navigation = NavigationType.new(@content_item.content_item)
-
     # Setting a variant on a request is a type of Rails Dark Magic that will
     # use a convention to automagically load an alternative partial, view or
     # layout.  For example, if I set a variant of :taxonomy_navigation and we render
     # a partial called _breadcrumbs.html.erb then Rails will attempt to load
     # _breadcrumbs.html+taxonomy_navigation.erb instead. If this file doesn't exist,
     # then it falls back to _breadcrumbs.html.erb.  See:
     # http://edgeguides.rubyonrails.org/4_1_release_notes.html#action-pack-variants
-    if @navigation.should_present_taxonomy_navigation?
-      request.variant = :taxonomy_navigation
+    if should_present_universal_navigation?
+      request.variant = :universal_navigation
+    else
+      @navigation = NavigationType.new(@content_item.content_item)
+      if @navigation.should_present_taxonomy_navigation?
+        request.variant = :taxonomy_navigation
+      end
     end
   end
 
@@ -111,6 +116,10 @@ def setup_tasklist_ab_testing
     set_tasklist_response_header
   end
 
+  def setup_content_navigation_ab_testing
+    set_content_navigation_response_header
+  end
+
   def content_item_path
     path_and_optional_locale = params
                                  .values_at(:path, :locale)

app/presenters/content_item_presenter.rb

@@ -62,6 +62,10 @@ def related_items
     @nav_helper.related_items
   end
 
+  def tagged_to_a_taxon?
+    content_item.dig("links", "taxons").present?
+  end
+
 private
 
   def display_date(timestamp, format = "%-d %B %Y")

app/views/layouts/application.html.erb

@@ -25,6 +25,7 @@
   <% end %>
   <meta name="govuk:content-id" content="<%= @content_item.content_id %>" />
   <%= tasklist_variant.analytics_meta_tag.html_safe if tasklist_ab_test_applies? %>
+  <%= content_navigation_variant.analytics_meta_tag.html_safe if content_navigation_ab_test_applies? %>
   <%= yield :extra_head_content %>
 </head>
 <body>

test/controllers/content_navigation_ab_testing_content_items_controller_test.rb

@@ -0,0 +1,69 @@
+require 'test_helper'
+
+class ContentItemsControllerTest < ActionController::TestCase
+  include GdsApi::TestHelpers::ContentStore
+  include GovukAbTesting::MinitestHelpers
+
+  ContentItemsController::GUIDANCE_DOCUMENT_TYPES.each do |document_type|
+    schema_name = document_type == 'statutory_guidance' ? 'publication' : document_type
+
+    test "does not show universal navigation when no taxons are tagged to #{document_type}" do
+      content_item = content_store_has_schema_example(schema_name, schema_name)
+      path = "government/abtest/#{schema_name}"
+      content_item['base_path'] = "/#{path}"
+      content_item['links'] = {}
+
+      content_store_has_item(content_item['base_path'], content_item)
+
+      setup_ab_variant('ContentNavigation', ContentItemsController::CONTENT_NAVIGATION_ORIGINAL)
+      get :show, params: { path: path }
+      assert_equal [], @request.variant
+      assert_response_not_modified_for_ab_test('ContentNavigation')
+    end
+
+    test "#{document_type} honours content navigation AB Testing cookie" do
+      content_item = content_store_has_schema_example(schema_name, schema_name)
+      path = "government/abtest/#{schema_name}"
+      content_item['document_type'] = document_type
+      content_item['base_path'] = "/#{path}"
+      content_item['links'] = {
+        'taxons' => [
+          {
+            'title' => 'A Taxon',
+            'base_path' => '/a-taxon',
+          }
+        ]
+      }
+
+      content_store_has_item(content_item['base_path'], content_item)
+
+      ContentItemsController::CONTENT_NAVIGATION_ALLOWED_VARIANTS.each do |variant|
+        with_variant ContentNavigation: variant do
+          get :show, params: { path: path }
+          requested = @controller.content_navigation_ab_test.requested_variant(request.headers)
+          assert_response 200
+          assert requested.variant?(variant)
+
+          if variant == ContentItemsController::CONTENT_NAVIGATION_ORIGINAL
+            assert_equal [:taxonomy_navigation], @request.variant
+          else
+            assert_equal [:universal_navigation], @request.variant
+          end
+        end
+      end
+    end
+
+    test "defaults to original view without AB testing cookie for #{document_type}" do
+      content_item = content_store_has_schema_example(schema_name, schema_name)
+      path = "government/abtest/#{schema_name}"
+      content_item['document_type'] = document_type
+      content_item['base_path'] = "/#{path}"
+      content_item['links'] = {}
+      content_store_has_item(content_item['base_path'], content_item)
+
+      get :show, params: { path: path }
+      assert_response 200
+      assert_equal [], @request.variant
+    end
+  end
+end