[Jest] Automate your migration to Jest using codemods
Jest is a fantastic testing library, but maybe you've been putting off the switch because migrating all of your existing tests from another library seems like a daunting task. With jest-codemods, you can automate most, if not all, of that migration! The jest-codemods CLI is a wrapper around jscodeshift that is specifically focused on helping you migrate from several popular test runner and assertion library combinations to Jest. In this lesson, we'll walk through converting a small sampling of tests created with Mocha, Sinon and Chai over to Jest. We'll even take a look at a couple edge cases where the conversion requires some manual intervention so you can be prepared for those in your own project.
Install:
npm i -D jest
npm i -g jest-codemons
Run:
jest-codemods # default path is under src
There is a waring:
"
jest-codemods warning: (src/index.spec.js) Usage of package "sinon" might be incompatible with Jest
"
describe('once', () => { test('Only invokes the function once', () => { const fn = sinon.stub() const onceFn = once(fn) onceFn() onceFn() onceFn() onceFn() sinon.assert.calledOnce(fn) }) })
Change to:
describe('once', () => { test('Only invokes the function once', () => { const fn = jest.fn(); const onceFn = once(fn) onceFn() onceFn() onceFn() onceFn() expect(fn).toHaveBeenCalledTimes(1); }) })
One failed test:
expect(result).to.eq(3)
Change to:
expect(result).toBe(3)
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