DEV: Use serializers for user_notification_schedule and featured_topic (#27719)

Co-authored-by: Alan Guo Xiang Tan <gxtan1990@gmail.com>

spec/serializers/user_card_serializer_spec.rb

@@ -126,4 +126,27 @@ RSpec.describe UserCardSerializer do
       expect(json.keys).not_to include :status
     end
   end
+
+  describe "#featured_topic" do
+    fab!(:user)
+    fab!(:featured_topic) { Fabricate(:topic) }
+
+    before { user.user_profile.update(featured_topic_id: featured_topic.id) }
+
+    it "includes the featured topic" do
+      serializer = described_class.new(user, scope: Guardian.new(user), root: false)
+      json = serializer.as_json
+
+      expect(json[:featured_topic]).to_not be_nil
+      expect(json[:featured_topic][:id]).to eq(featured_topic.id)
+      expect(json[:featured_topic][:title]).to eq(featured_topic.title)
+      expect(json[:featured_topic].keys).to contain_exactly(
+        :id,
+        :title,
+        :fancy_title,
+        :slug,
+        :posts_count,
+      )
+    end
+  end
 end