Here is my Heian Shodan karate app with the Test Drive Now option (click here to go to the test drive).
Here is a short video of the "app simulation" directly from the Amazon App Store. The "finger" on the screen is actually my mouse moving left to right.
How do they do it? I wasn't sure, so I checked on the Amazon website and found this:
Clicking the “Test drive now” button launches a copy of this app on Amazon Elastic Compute Cloud (EC2), a web service that provides on-demand compute capacity in the cloud for developers. When you click on the simulated phone using your mouse, we send those inputs over the Internet to the app running on Amazon EC2 — just like your mobile device would send a finger tap to the app. Our servers then send the video and audio output from the app back to your computer. All this happens in real time, allowing you to explore the features of the app as if it were running on your mobile device.