jest/docs/Architecture.md

id	title
architecture	Architecture

If you are interested in learning more about how Jest works, understand its architecture, and how Jest is split up into individual reusable packages, check out this video:

If you'd like to learn how to build a testing framework like Jest from scratch, check out this video:

There is also a written guide you can follow. It teaches the fundamental concepts of Jest and explains how various parts of Jest can be used to compose a custom testing framework.