create-jest-runner

A highly opinionated way for creating Jest Runners

Install

yarn add create-jest-runner

Usage

create-jest-runner takes care of handling the appropriate parallelization and creating a worker farm for your runner.

You simply need two files:

• Entry file: Used by Jest as an entrypoint to your runner.
• Run file: Runs once per test file, and it encapsulates the logic of your runner

1) Create your entry file

// index.js
const { createJestRunner } = require('create-jest-runner');
module.exports = createJestRunner(require.resolve('./run'));

2) Create your run file

module.exports = (options) => {
};

Run File API

This file should export a function that receives one parameter with the options

options: { testPath, config, globalConfig }

• testPath: Path of the file that is going to be tests
• config: Jest Project config used by this file
• globalConfig: Jest global config

You can return one of the following values:

• testResult: Needs to be an object of type https://github.com/facebook/jest/blob/master/types/TestResult.js#L131-L157
• Promise<testResult|Error>: needs to be of above type.
• Error: good for reporting system error, not failed tests.

Example of a runner

This runner "blade-runner" makes sure that these two emojis ⚔️ 🏃 are present in every file

// index.js
const { createJestRunner } = require('create-jest-runner');
module.exports = createJestRunner(require.resolve('./run'));

// run.js
const fs = require('fs');
const { pass, fail } = require('create-jest-runner');

module.exports = ({ testPath }) => {
  const start = +new Date();
  const contents = fs.readFileSync(testPath, 'utf8');
  const end = +new Date();

  if (contents.includes('⚔️🏃')) {
    return pass({ start, end, test: { path: testPath } });
  }
  const errorMessage = 'Company policies require ⚔️ 🏃 in every file';
  return fail({
    start,
    end,
    test: { path: testPath, errorMessage, title: 'Check for ⚔️ 🏃' },
  });
};

Add your runner to Jest config

Once you have your Jest runner you can add it to your Jest config.

In your package.json

{
  "jest": {
    "runner": "/path/to/my-runner"
  }
}

Or in jest.config.js

module.exports = {
  runner: '/path/to/my-runner',
}

Run Jest

yarn jest