Thanks for all your suggestions. Adding more comments into source code of test suite is a good point.
But it’s hard to write too much words, especially hard to adding images in the source. So I wrote a catalog of docs’ plan
]Please give some comments, or edit this wiki page directly.
By the way, the catalog is too large, almost equal to a book. It seems hard to be achieved only by core developers. I’m not sure if anyone interest in writing it together?