Learning Assistants Using Mocha

it "should have edit button if user has permission to edit" do
  EntitiesHelper.stubs(:permission_to_edit_entity?).returns(true)
  get :index
  @entities[0..3].each do |entity|
    response.should have_selector("form",
      :method => "get",
      :action => "/entities/edit/#{entity[:id]}") do |form|
        form.should have_selector("input", :value => "Edit")
    end
  end
end

I am trying to write a simple test case that checks that the edit button is displayed if the user has permission to edit. I am trying to use stubbing for this. However, this does not seem to work. In the output view, the edit button does not appear next to each individual entity that I expect if stubbing works. I'm new to mocha and insult - am I doing something wrong?

Thank!