This app was written to verify a system bug.
When uninstall an app or update an app, there may be some files left in the folder /data/data/<app package name>. If that case happened, you can not install the app again because of the error "INSTALL_FAILED_UID_CHANGED". If your device is rooted, then you can remove the app data folder manually. Otherwise, you have to do factory data reset in order to install the app again.