Sean, the beginning of material design. Before that, yes, it was a mess. It was still a mess when you had to support 4.x. It was an absolute shitshow when you had to support 2.x (your app would sometimes crash on some devices somewhere deep inside TextView because they implemented their own buggy support for emoji).
CTS is a test suite that an OEM skin must fully pass to be officially considered Android and allowed to ship with Google apps. It very thoroughly tests all public APIs in that they all behave as specified in the docs.
Sean, the beginning of material design. Before that, yes, it was a mess. It was still a mess when you had to support 4.x. It was an absolute shitshow when you had to support 2.x (your app would sometimes crash on some devices somewhere deep inside TextView because they implemented their own buggy support for emoji).
Sean, no. Material design themes are part of Google's CTS from the beginning.