Android Comparability Test Suite, a suite of several thousand test cases to be run on an Android device from a host computer to test the OS and to ensure compatibility across Android implementations.
CTS is part of the AOSP's Comparability Program. As of Android 4.0.3 (ICS), it is included in the open source project. Binaries of prior version may be downloaded from the Android Open Source site.
CTS can also be used to add custom tests to internal Android builds.