it "Should send the calls mp3 file" do
    File.should_receive(:exist?).with("#{RAILS_ROOT}/public/audio/call_#{@call.id}.mp3").and_return(true)
    controller.should_receive(:send_file).with("/foo.mp3", anything())

    get :listen, :id => "1"

    assigns.should have_key(:call)
    assigns[:call].should equal(@call)
  end

def listen
  @call = something something params[:id]
  path = File.join(#{RAILS_ROOT}, "public", "audio", "call_#{@call.id}.mp3")
  if File.exist?(path)
    send_file(path)
  end
end