module Tins::DateTimeDummy

def self.included(modul)
  class << modul
    alias really_now now
    remove_method :now rescue nil
    attr_writer :dummy
    def dummy(value = nil)
      if value.nil?
        @dummy
      else
        begin
          old_dummy = @dummy
          @dummy = value
          yield
        ensure
          @dummy = old_dummy
        end
      end
    end
    def now
      if dummy
        dummy.dup
      else
        really_now
      end
    end
  end
  super
end