activerecord/test/cases/xml_serialization_test.rb

output.xml

<?xml version="1.0" encoding="UTF-8"?>
<toy>
  <created-at type="datetime">2010-11-30T19:00:36-08:00</created-at>
  <integer type="integer" nil="true"></integer>
  <name>Mickey</name>
  <pet-id type="integer" nil="true"></pet-id>
  <toy-id type="integer">1</toy-id>
  <updated-at type="datetime">2006-08-01T00:00:00Z</updated-at>
</toy>

<?xml version="1.0" encoding="UTF-8"?>
<toy>
  <created-at type="datetime">2010-11-30T19:00:36-08:00</created-at>
  <integer type="integer" nil="true"></integer>
  <name>Minnie</name>
  <pet-id type="integer" nil="true"></pet-id>
  <toy-id type="integer">2</toy-id>
  <updated-at type="datetime">2006-07-31T17:00:00-07:00</updated-at>
</toy>

xml.rb

module ActiveModel
  # == Active Model XML Serializer
  module Serializers
    module Xml 
      extend ActiveSupport::Concern
      include ActiveModel::Serialization

      class Serializer #:nodoc:
        class Attribute #:nodoc:
          attr_reader :name, :value, :type

          def initialize(name, serializable, raw_value=nil)
            @name, @serializable = name, serializable

            ### The following line seems to fix the tests.
            raw_value = raw_value.in_time_zone if raw_value.respond_to?(:in_time_zone)

            @value = raw_value || @serializable.send(name)
            @type  = compute_type
          end 

xml_serialization_test.rb

require 'models/toy'

class DefaultXmlSerializationTimezoneTest < ActiveRecord::TestCase
  def test_should_serialize_datetime_with_timezone
    timezone, Time.zone = Time.zone, "Pacific Time (US & Canada)"

    toy = Toy.create(:name => 'Mickey', :updated_at => Time.utc(2006, 8, 1))
    ### puts toy.to_xml
    assert_match %r{<updated-at type=\"datetime\">2006-07-31T17:00:00-07:00</updated-at>}, toy.to_xml
  ensure
    Time.zone = timezone
  end

  def test_should_serialize_datetime_with_timezone_reloaded
    timezone, Time.zone = Time.zone, "Pacific Time (US & Canada)"

    toy = Toy.create(:name => 'Minnie', :updated_at => Time.utc(2006, 8, 1)).reload
    ### puts toy.to_xml
    assert_match %r{<updated-at type=\"datetime\">2006-07-31T17:00:00-07:00</updated-at>}, toy.to_xml
  ensure
    Time.zone = timezone
  end
end