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

spec/serializers/rest/muted_account_serializer_spec.rb

@@ -0,0 +1,42 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+RSpec.describe REST::MutedAccountSerializer do
+  subject do
+    serialized_record_json(
+      mutee,
+      described_class,
+      options: {
+        scope: current_user,
+        scope_name: :current_user,
+      }
+    )
+  end
+
+  let(:current_user) { Fabricate(:user) }
+  let(:account) { current_user.account }
+  let(:mutee) { Fabricate(:account, username: 'mutee') }
+
+  context 'when mute_expires_at is populated and non-nil' do
+    before do
+      account.follow!(mutee)
+      account.mute!(mutee, duration: 1.day)
+    end
+
+    it 'parses as RFC 3339 datetime' do
+      expect { DateTime.rfc3339(subject['mute_expires_at']) }.to_not raise_error
+    end
+  end
+
+  context 'when mute has no duration' do
+    before do
+      account.follow!(mutee)
+      account.mute!(mutee)
+    end
+
+    it 'has a nil mute_expires_at' do
+      expect(subject['mute_expires_at']).to be_nil
+    end
+  end
+end