me

application_helper_spec.rb

    let(:post) { create :post, body: "Blah en *narf*" }

    it "let's Kramdown do the heavy lifting" do
      kramdown = double
      kramdown.should_receive(:to_html)
      Kramdown::Document.should_receive(:new).with(post.body).and_return(kramdown)

      helper.markdown(post.body)
    end

Why spec the helper implementation instead of its behaviour? Also, why use a post at all? Why not say:

expect(helper.markdown("Blah en *narf*")).to eql("<p>Blah en <em>narf</em></p>\n")