Codemods are small programs that help you automate changes to your codebase. Think of them as search and replace on steroids.

We made jest-codemods so you can try out Jest on your existing codebase. We strive to make the migration as smooth as possible, but some manual intervention and tweaks to your tests are to be expected.

Usage (CLI)

To use the interactive CLI run

$ npx jest-codemods

If you do not have npx installed, you can install the jest-codemods command globally by running npm install -g jest-codemods.

For more options

$ npx jest-codemods --help

    Usage:      npx jest-codemods <path> [options]

    Examples:   npx jest-codemods src
                npx jest-codemods src/**/*.test.js

    Options:
      -f, --force       Bypass Git safety checks and force codemods to run
      -d, --dry         Dry run (no changes are made to files)

To transform all test files in a directory run jest-codemods . in your terminal.

Notice the console output for errors, manual intervention and tweaks might be required.

Usage (jscodeshift)

To make the process as simple as possible, we recommend the jest-codemods CLI that wraps the jscodeshift executable. But you can also run the transformations directly using jscodeshift.

$ npm install -g jscodeshift
$ npm install jest-codemods
$ jscodeshift -t node_modules/jest-codemods/dist/transformers/ava.js test-folder
$ jscodeshift -t node_modules/jest-codemods/dist/transformers/chai-assert.js test-folder
$ jscodeshift -t node_modules/jest-codemods/dist/transformers/chai-should.js test-folder
$ jscodeshift -t node_modules/jest-codemods/dist/transformers/expect-js.js test-folder
$ jscodeshift -t node_modules/jest-codemods/dist/transformers/expect.js test-folder
$ jscodeshift -t node_modules/jest-codemods/dist/transformers/jasmine-globals.js test-folder
$ jscodeshift -t node_modules/jest-codemods/dist/transformers/jasmine-this.js test-folder
$ jscodeshift -t node_modules/jest-codemods/dist/transformers/mocha.js test-folder
$ jscodeshift -t node_modules/jest-codemods/dist/transformers/should.js test-folder
$ jscodeshift -t node_modules/jest-codemods/dist/transformers/tape.js test-folder

Test environment: Jest on Node.js or other

If you're using Jest as your test runner and executing tests on Node.js, you'll want to use the default option when prompted. In this case, jest-codemods assumes that global values such as expect and jest are provided and will not require() them explicitly.

If, however, you are using a different test runner or executing Jest tests in a browser, you may need to choose the option with explicit require() calls.

In the second case, after running jest-codemods, you might need to install a few dependencies:

yarn add --dev expect jest-mock

npm install --save-dev expect jest-mock

Transformations

If possible import / require statements determine if any transformation are carried out. The original code quoting style is preserved. Warnings are made if packages are used that are incompatible with Jest.

Inspiration

Thanks to avajs/ava-codemods for inspiration and original CLI setup.

The Mocha and Chai assert support began its life at paularmstrong/mocha-to-jest-codemod.

Chai Should/Expect came from AlexJuarez/chai-to-jasmine.

Links

• Official Jest migration guide https://jestjs.io/docs/en/migration-guide
• "Migrating 2,000+ Specs from Karma to Jest" https://labs.contactually.com/migrating-2-000-specs-from-karma-to-jest-25dd8b0f3cfb
• "Into the Great Unknown — Migrating from Mocha to Jest" https://ebaytech.berlin/into-the-great-unknown-migrating-from-mocha-to-jest-3baced083c7e
• "Automate your migration to Jest using codemods" Egghead video https://egghead.io/lessons/jest-automate-your-migration-to-jest-using-codemods
• "Migrating Ava to Jest" https://codedaily.io/tutorials/11/Migrating-Ava-to-Jest
• "Switching from Ava to Jest for TypeScript" https://shift.infinite.red/switching-from-ava-to-jest-for-typescript-a6dac7d1712f
• "Migrating a Mocha project to Jest Test Framework" https://medium.com/@liran.tal/migrating-a-mocha-project-to-jest-test-framework-76d13d76685
• "Migrating to Jest on the P2P team at PayPal" https://blog.kentcdodds.com/migrating-to-jest-881f75366e7e

Contributing

To get started, run:

yarn

When developing:

yarn verify  # (build/lint/test)
yarn build
yarn lint
yarn test
yarn test:cov
yarn test:watch

License

MIT