stub_base.rb

class MyDir < Dir
  class << self
    def [](args)
      super(args).collect {|entry| do_junk(entry)}
    end
  end
end

describe MyDir
  before do
    Dir.stub(:[]).and_return(%w(file1 file2))
  end

  it do
    MyDir['*'].should # undefine method [] for MyDir
  end
end