Recording the screen of a mobile device is not an easy thing. You can build a fancy test rig, with cameras and so on. But it's expensive and cumbersome. There are iOS apps that let you record the screen. But the ones I've seen are either buggy as hell or require you to jailbreak your device.
But today I came across another option. AirPlay lets you mirror your iPhone or iPad's display on an Apple TV. But you can also mirror it on a Mac, using a product called AirServer. The company that created it promotes it as a way to play multi-player games with your friends on a nice big screen.
But with your device's screen mirrored on your Mac, you can use screen-recording software (like Screenflow, Camtasia, or Morae) to record it. Which, for user testing, is pretty damn handy. (The image above was captured from my Mac's screen.)
(Disclaimer: If you use the above link to download and install AirServer, my free trial gets extended by three days. Just so you know.)