def pdf
     respond_to do |format|
      format.pdf do
        @pdf = ApplicationController.render pdf: some_number,
                                template: "show",
                                layout: nil
        send_data(@pdf, :filename => "something.pdf", :type => "application/pdf", disposition: 'attachment')
      end
     end
   end

  path "/pdf" do
    get "return PDF" do
      produces 'application/pdf'
      response '200', 'PDF generated' do
        schema type: :file
        before do |example|
          sign_in @some_user
          submit_request(example.metadata)
        end
        it 'returns a 200 response' do |example|
          assert_response_matches_metadata(example.metadata)
        end
      end
    end
  end

path "/pdf.pdf" do
   ...
end