time_zone_test_helper.rb

#
# Put this to test/time_zone_test_helper.rb and include the module into Your
# base TestCase class e.g. test_helper.rb :
#
#   require 'time_zone_test_helper'
#
#   class ActiveSupport::TestCase
#
#     include TimeZoneTestHelper
#     ...
#
# Now, in a time zone sensitive test case use the local time zone for tests :
#
#   class MyTestCase < ActiveSupport::TestCase
#
#     use_local_time_zone_for_tests
#     ...
#
#   end
#
module TimeZoneTestHelper

  def self.included(base)
    base.extend ClassMethods
  end

  module ClassMethods

    def use_local_time_zone_for_tests
      self.send :setup, :setup_local_time_zone
      self.send :teardown, :reset_local_time_zone
    end

  end

  def setup_local_time_zone
    Time.zone = local_time_zone
  end

  def reset_local_time_zone
    Time.zone = nil
  end

  private

    def local_time_zone
      ActiveSupport::TimeZone[Time.now.utc_offset]
    end

end