blog post: http://autonomousmachine.com/2008/10/1/simple-rspec-markup-matcher

gistfile1.rbx

it "should wrap with a div" do
  input = <<-HTML
    <p>
        In order to attain the greatest possible clearness,
        let us return to our example of the railway carriage supposed
        to be travelling uniformly.
    </p>
  HTML
  
  output = <<-HTML
      <div class="klass" id="div_3">
        <p>
          In order to attain the greatest possible clearness,
          let us return to our example of the railway carriage supposed
          to be travelling uniformly.
        </p>
      </div>  
  HTML
  
  wrap_with_div(input, :class => 'klass', :id => 'div_3').should match_markup(output)
end