While writing functional tests, I use assert_tag a lot. Many times the assertion fails and debugging with ‘response text’ dump on terminal is not easy. It would be much easier to debug if the response text is opened in a browser. This is how that can be done.

In your test/test_helper.rb add a new method called show_response.

class Test::Unit::TestCase
  def show_response
    Dir.mkdir(File.join(RAILS_ROOT, 'tmp')) unless File.directory?(File.join(RAILS_ROOT,'tmp'))
    response_html = File.join(RAILS_ROOT, 'tmp', 'response.html')
    File.open(response_html,'w') { |f| f.write(@response.body) }
    system 'open ' + File.expand_path(response_html) rescue nil
  end
end

This is how I use this method while debugging.

context 'get show for comment which belongs to another class' do
  setup do
    @comment = Factory(:comment, :article => @article)
    get :show, {:id => @comment.id, :klass => @comment.class.name.underscore }
    show_response
  end
  should_respond_with :success
  should 'have belongs_to message' do
    assert_tag( :tag => 'p',
                :attributes => {:class => 'belongs_to'},
                :descendant => {:tag => 'a', :child => /Article/})
  end
end

If you are using mac then running this test will open a new web page with full response text. Now I can easily see why my assertion might be failing. show_response also works with ajax request.