RSpec should automatically load classes and modules from your rails environment when you 'describe' them, so a valid helper spec could be:
#deleted
But remember that bdd is not testing every single method but the behaviour of your application.
edit:
as @Ken said, my spec was not correct, It was definately the wrong way to do it. So I came out with a Request spec solution that I like more than an Helper spec.
# inside your helper
def title(page_title)
content_for(:title) { page_title }
end
# views/resource/index.html.*
<%= title "foo" %>
# request spec
require 'spec_helper'
describe YourResource do
it "should output content for title"
get "/resource"
response.body.should =~ /<title>foo<\/title>/
end
end
otherwise, if you want to test only the helper behavior (because it's critical or because you don't have any views) @Ken's solution is better.