This paper proposes Mimic, an automated UI com- patibility testing system for Android apps. Mimic is designed specifically for comparing the UI behavior of an app across different devices, different Android versions, and different app versions. This design choice stems from a common problem that Android developers and researchers face—how to test whether or not an app behaves consistently across different environments or internal changes. Mimic allows Android app developers to easily perform backward and forward compatibility testing for their apps. It also enables a clear comparison between a stable version of app and a newer version of app. In doing so, Mimic allows multiple testing strategies to be used, such as randomized or sequential testing. Finally, Mimic programming model allows such tests to be scripted with much less developer effort than other comparable systems. Additionally, Mimic allows parallel testing with multiple testing devices and thereby speeds up testing time. To demonstrate these capabilities, we perform extensive tests for each of the scenarios described above. Our results show that Mimic is effective in detecting forward and backward compatibility issues, and verify runtime behavior of apps. Our evaluation also shows that Mimic significantly reduces the development burden for developers.