JS Testing with Jest and React

Published Thursday, April 05, 2018

A code reading by @gj

Jest

• New hotness for testing React
• More or less a superset of Jasmine
• Backed by Facebook
• “Just works” out of the box
• Started as a wrapper around JSDom, evolved into its own thing

Hopes and dreams: Jest makes test writing fun and easy => we write more tests

Helpful features

1. Watch mode (--watch) - runs test on code changes (similar to guard on server-side)
2. Coverage metrics (--coverage) - out of the box
3. Notifications mode (--notify) - native OS notification when test runs completes
4. Tracks test failures - runs failed tests first on next run (shorter feedback loop)
5. Tracks test suite run time - suites run in parallel across processes
6. Fully sandboxed - tests are strictly scoped, so no globals pollution

Suggestions

1. Enzyme’s shallow over mount for rendering components

WIP… more to follow after next week’s code reading.