Android Compatibility Definition Document (CDD) provides requirements, recommendations and guidelines to manufacturers who want their devices to be compatible with certain release of Android. It allows them to pass Google’s CTS (Compatibility Test Suite). To be compatible with Android, the smartphone or tablet must meet all requirements set in this Compatibility Definition Document, including all documents incorporated by reference. For each release of the Android platform, Google provides a new Compatibility Definition Document.
The main goal of CDD is to be comprehensive about the minimum required hardware features such as display density, keyboards, etc. The software tests cannot verify that all of them meet the Android compatibility requirements. Moreover, it’s impossible to test them by CTS. For example, the Compatibility Test Suite includes a test that verifies for the correct behavior and presence of OpenGL graphics APIs, but no software test can verify that the graphics appear correctly on the display.
The role of CDD is to eliminate ambiguity and clarify specific requirements. The document is not comprehensive about all required features, because the Android platform is an open-source code and the code itself is enough to represent the “specification” of the platform and its APIs.