Jot Thought

On a recent Ruby on Rails project, we ran into a situation where we needed to use the ActionController::Base url_for method in our tests. My first attempt was to simply write the test as follows:

def test_next__should_show_step3
  @request.env["HTTP_REFERER"] = @controller.url_for(
    :controller => 'wizard',
    :action => 'step',
    :step_number => "1",
    :id => 1)
 
  post :next, :id => 1
  assert_not_nil
  assigns(:virtual_tour)
  assert_response :redirect
  assert_redirected_to :action => 'step', :step_number => "3", :id => assigns(:virtual_tour).id
end

When I ran the test it resulted in the following error:

test_next__should_show_step3(VirtualTourWizardControllerTest):
NoMethodError: You have a nil object when you didn't expect it! The error occured while evaluating nil.rewrite
/usr/local/lib/ruby/gems/1.8/gems/actionpack-1.12.5/lib/action_controller/base.rb:488:in `url_for'
./test/functional/virtual_tour_wizard_controller_test.rb:91:in `set_referer_step'
./test/functional/virtual_tour_wizard_controller_test.rb:64:in `test_next__should_update_virtual_tour'

When we looked at the rails code, we saw that an instance variable @url was not initialized yet in our tests. This was causing the nil error seen above. We found a post that wrote about a work around by initializing this variable by calling get :index or some other action that doesn’t cause a side effect. This seems like a bit of a hack so we dug a little further.

After a little digging in the rails source code, we found the class that does the actual URL rewriting. The class is called ActionController::UrlRewriter which url_for delegates to to do the actual URL rewriting. So we created a little helper method in test_helper.rb to wrap ActionController::UrlRewriter in a nice helper method called url_for. The following is the method we created in test_helper.rb

def url_for(options)
  url = ActionController::UrlRewriter.new(@request, nil)
  url.rewrite(options)
end

We can know rewrite our test to look like this.

def test_next__should_show_step3
  @request.env["HTTP_REFERER"] = url_for(
    :controller => 'wizard',
    :action => 'step',
    :step_number => "1",
    :id => 1)
 
  post :next, :id => 1
  assert_not_nil
  assigns(:virtual_tour)
  assert_response :redirect
  assert_redirected_to :action => 'step', :step_number => "3", :id => assigns(:virtual_tour).id
end

We ended up doing a little more refactoring after this since we set the referer like this in many of our other tests.