An issue with Rspec on Windows

Rspec is a very popular test framework used to test Rails application. I have tried to install and use it for my Rails projects on Windows. It raised a bug when I ran tests:

c:/Ruby/lib/ruby/gems/1.8/gems/activesupport-2.3.5/lib/active_support/dependencies.rb:440:in load_missing_constant': uninitialized constant RbReadline::Encoding (NameError)

from c:/Ruby/lib/ruby/site_ruby/1.8/rbreadline.rb:4404 

I traced back and found these causing lines:

   if defined? ''.getbyte
      @encoding = "X"      # ruby 1.9.x or greater
      @encoding_name = Encoding.default_external.to_s
   end

It seems the Rspec uses Ruby Readline library for its command-line interface. It defined getbyte that uses Encoding module which hasn't been defined in this Ruby package on Windows. I then commented out the line using Encoding module and the bug get fixed...

   if defined? ''.getbyte
      @encoding = "X"      # ruby 1.9.x or greater
      # @encoding_name = Encoding.default_external.to_s
   end

It's not common to pass over the issue by this way but hopefully it still works fine in my case.