How are the internal components of Android such as Zygote and Binder tested before being released?
I tried looking around for answers to this but most resources (blog posts and research papers) I could find dealt mostly with Android application testing and/or verification techniques for Android applications and not the system itself.
A (somewhat) related official information I found was Android Compatibility Test Suite(CTS). I suppose this is aimed at hardware vendors who customize AOSP code for their devices. CTS performs high level compatibility checks from user applications only but not all code of internal components is tested.
If there are no publicly known techniques currently being used in Android, are there any known techniques proposed for other operating systems which would be applicable for Android?
I am working on replacing some components of Android entirely and looking for efficient ways to test them (correctness, compatibility, security and more perhaps).
Edit: It is sufficient for me to know how internal components of Android such as Zygote and Binder are tested when changes are made to them. Since they are internal components, the testing could be very likely automated. Also, I am hoping to replacing these components with functionally equivalent code so these tests will help establish that no critical functionality has been affected.