Testing ANY helper in a functional test

Recipe #44 - "Write Tests for Your Helpers" in the book "Rails recipes" instructs us doing this by including helper modules in subclasses of Test::Unit::TestCase. However it wouldn't work if a helper you want to test is implemented with _erbout for example. I have just faced this issue last week, then my colleague suggested me like that "Don't you render it in a view?" (in Japanese). Yes, in a view biding, every helpers must be work correctly.

The solution is like following code:

test/units/foo_helper_test.rb:
...

class FooTestController < ActionController::Base
  ...
  def index
    render :inline => <<-INLINE
      <% foo do %>
          <%= ... %>
      <% end %>
    INLINE
  end

end

class FooHelperTest < Test::Unit::TestCase
  def setup
    @controller = FooTestController.new
    @request    = ActionController::TestRequest.new
    @response   = ActionController::TestResponse.new
  end

  def test_foo
    get :index
    # do assert_select or whatever you like, to check rendering result of the helper.
  end  
end