How to migrate from mocha to jest in 15 easy steps - and why

For a long time I looked at the jest testing framework, which has a huge amount of all kinds of tasty chips, one of which is multi-threaded test execution. Provided that I had a project for 5000 unit tests, migration promised to be extremely useful. Next, I will describe 14 simple steps for which I managed to migrate - albeit with some reservations - and what we got as a result. Spoiler - everything turned out very cool.

Baseline

— , , . — — . , , 5000 — .

mocha, chai, sinon, rewire, nock, nyc — , . , :

1) sandbox, , sinon.sandbox.
2) - — . , .
3) sinon.useFakeTimers. . .
4) 13 . , , 13 .

, Jest , . puppeteer , ( ) — — , . — . , — , .

- mocha — , , . , mocha-parallel-tests , . — , , . , .

jest-codemods — , , — sinon — 5000 . .

!

1.

awesome-jest, jest-runner-mocha. " !" — , , .

.

npm install --save-dev jest jest-runner-mocha

jest-test.config.js

module.exports = {
    runner: 'jest-runner-mocha',
    testRegex: 'tests/.*test_.*\\.js$',
    maxWorkers: 3
};

node --use_strict ./node_modules/.bin/jest --no-cache --config jest-test.config.js

, , .
, — jest. — .
— — 90% , ! , — , .

2.

, , . , , — , . , , . jest-dot-reporter — progress bar , — .

CLI config:

    reporters: ['jest-dot-reporter'],

, awesome-jest - . — .

3. mocha

— , . jest-runner-mocha. , mocha 3.5. — 7. , Node 4. ,

• Node 4 mocha jest, yarn,
• Node 8 End Of Life
• ,
• mocha peerDependency,

. . . peerDependency — , .

4. clearMocks

, . — — . — , — , .

, , clearMocks . , — , . jasmine2. — .

— setupFilesAfterEnv, — clearMocks — . , . , clearMocks jest — sinon, jest .

:

    setupFilesAfterEnv: [ 'lib/clearMocks.js'],
    clearMocks: true,

lib/clearMocks.js

// const jest = require('jest-mock');
const sinon = require('sinon');

module.exports = {
    clearMocks: () => {
        // jest.clearAllMocks(); ,     ,  
        sinon.sandbox.restore();
    }
};

.
. , — .

5.

, - . , , ( ). . , . — ! , ? , !

6.

, process 500 exit. - .

process.on('exit', () => process.exit());

, , … , , … slowpoke.jpg.

7.

, , , process unCaughtException. , , — 7.0.0 7.0.1.

8.

, — , . jest-runner-mocha, jest . , — — . — , , yarn.

9.

, postinstall hook jest-runner-mocha:

> core-js@3.6.4 postinstall 
> node -e "try{require('./postinstall')}catch(e){}"

Thank you for using core-js ( https://github.com/zloirock/core-js ) for polyfilling JavaScript standard library!

The project needs your help! Please consider supporting of core-js on Open Collective or Patreon: 
> https://opencollective.com/core-js 
> https://www.patreon.com/zloirock 

Also, the author of core-js ( https://github.com/zloirock ) is looking for a good job -)

, , . . — c 23,528,407 , — , , , . , 57 , . . . 12 . , . . . . , , .

— .

10.

, — . CI , , , . - esprint — , .

jest-runner-eslint — , , . , . , — .

, , — . Jest , grunt gulp. , , , . Jest , ...

11. CI

CI , - . , , , . — !

12.

- , . - , … , yarn, yarn.lock. . .

. yarn — yarn . . ? , — .

? , yarn package-lock.json, npm-shrinkwrap.json ( ). — , shrinkwrap — , shrinkwrap. , , . , , . npm prune --production.

, . , , . , . - . , . ?

13.

, — . , . , jest , . , .

14.

, , , — , . , .

15.

. , . !

?

1. CI 3 3 . , , .
2. . — . , .
3. jest , .

ToDo

:

1. , . , . , mocha , .
2. jest — . — , .
3. , jest-codemods , — , .

Yes, if that, here is a link to my fork runner mocha .
You can put it with the command

npm install --save-dev @kernel-panic/jest-runner-mocha

And in the config register how

runner: '@kernel-panic/jest-runner-mocha',