Add a guide for testing with Jest

Borrowed from the thoughtbot guides with some removals that suite our
style.

README.md

@@ -42,6 +42,7 @@ do not cover your particular topic, review their guides for guidance.
 - [Rails](rails/README.md)
 - [React](react/README.md)
 - [Testing with RSpec](testing-rspec/README.md)
+- [Testing with Jest](testing-jest/README.md)
 
 ## Protocols
 

testing-jest/README.md

@@ -0,0 +1,19 @@
+# Testing with Jest
+
+- Use [eslint-plugin-jest] to enforce testing style
+- Use [@testing-library/jest-dom] for supplemental expectation matchers
+- Use [React Testing Library] for testing [React](/react/) components
+- Use [React Hooks Testing Library] for testing [React Hooks]
+- Use [User Event] for simulating DOM events on React components under test
+- Use [Fishery] for building factories
+- Prefer writing specific unit tests over [Snapshot Testing]
+- Prefer `describe` and `it` blocks over `test` blocks
+
+[eslint-plugin-jest]: https://github.com/jest-community/eslint-plugin-jest
+[testing-library/jest-dom]: https://github.com/testing-library/jest-dom
+[react testing library]: https://github.com/testing-library/react-testing-library
+[react hooks testing library]: https://github.com/testing-library/react-hooks-testing-library
+[react hooks]: https://reactjs.org/docs/hooks-overview.html
+[user event]: https://github.com/testing-library/user-event
+[fishery]: https://github.com/thoughtbot/fishery
+[snapshot testing]: https://jestjs.io/docs/en/snapshot-testing