Trying to extend ActionView::Helpers::FormBuilder

I am trying to DRY up some code by moving some logic into the FormBuilder. After reading the documentation about how to select and alternative form builder the logical solution for me seemed to be something like this. In the view ``` <% form_for @event, :builder => TestFormBuilder do |f| %> <%= f.test %> <%= f.submit 'Update' %> <% end %> ``` and then in app/helpers/application_helper.rb ``` module ApplicationHelper class TestFormBuilder < ActionView::Helpers::FormBuilder def test puts 'apa' end end end ``` This, however, gives me an error at the "form_for" ``` uninitialized constant ActionView::Base::CompiledTemplates::TestFormBuilder ``` Where am I doing it wrong?