Ensure datetime/date are serialized to correct format (#33086)

spec/serializers/rest/poll_serializer_spec.rb

@@ -0,0 +1,25 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+RSpec.describe REST::PollSerializer do
+  subject do
+    serialized_record_json(
+      poll,
+      described_class,
+      options: {
+        scope: current_user,
+        scope_name: :current_user,
+      }
+    )
+  end
+
+  let(:current_user) { Fabricate(:user) }
+  let(:poll) { Fabricate :poll }
+
+  context 'when expires_at is populated' do
+    it 'parses as RFC 3339 datetime' do
+      expect { DateTime.rfc3339(subject['expires_at']) }.to_not raise_error
+    end
+  end
+end