Add stub method for getting content that embeds a target

In Whitehall we use this method before all of our Cucumber tests as a default stub. This enables us to make our tests more concise. We can avoid having plumb this stub into various scenarios where the dependend content is not under tests. To do this we set up a stub that allows any content_id (via `anything`) so long as it looks like a uuid. If such a request is made we’ll return back an empty set of results.

lib/gds_api/test_helpers/publishing_api.rb

@@ -340,6 +340,43 @@ def stub_publishing_api_has_content(items, params = {})
           .to_return(status: 200, body: body.to_json, headers: {})
       end
 
+      # Stub GET /v2/content/:content_id/embedded to return a list of content items that embed the target content_id
+      #
+      # @example
+      #
+      #   stub_publishing_api_has_content_(
+      #     content_id: "9faacf5c-f4e6-4bf9-ba90-413e997c1f22" # this is the content_id for a reusable edition
+      #     total: 1 # the number of results returned
+      #     results: [{
+      #       "title" => "foo",
+      #       "document_type" => "document",
+      #       "base_path" => "/foo",
+      #       "content_id" => "e60fae2a-5490-4e2f-9e80-2093c47608d4",
+      #       "primary_publishing_organisation" => {
+      #         "content_id" => "7662e1e7-79f9-4d0a-b754-6232186851f6",
+      #         "title" => "bar",
+      #         "base_path" => "/organisation/bar",
+      #       },
+      #     }] # an array of content items that embed the target content_id
+      #   )
+      # @param content_id UUID
+      # @param total Integer
+      # @param params [Hash]
+      def stub_publishing_api_has_embedded_content(content_id:, total: 0, results: [])
+        url = if content_id.is_a?(Mocha::ParameterMatchers::Anything)
+                %r{\A#{PUBLISHING_API_V2_ENDPOINT}/content/[0-9a-fA-F-]{36}/embedded}
+              else
+                "#{PUBLISHING_API_V2_ENDPOINT}/content/#{content_id}/embedded"
+              end
+
+        stub_request(:get, url)
+          .to_return(body: {
+            "content_id" => content_id,
+            "total" => total,
+            "results" => results,
+          }.to_json)
+      end
+
       # This method has been refactored into publishing_api_has_content (above)
       # publishing_api_has_content allows for flexible passing in of arguments, please use instead
       def stub_publishing_api_has_fields_for_document(document_type, items, fields)