Test ES6 modules with Jest

Question

How to test ES6 modules with Jest.

Example:

sum.js

const sum = function (a, b) {
  return a + b;
}

export default sum;

sum.test.js

import sum from './sum';

test('adds 1 + 2 to equal 3', () => {
  expect(sum(1, 2)).toBe(3);
});

Paulo Coghi · Accepted Answer · 2019-09-16T10:12:22.747

33

The only requirement is to config your test environment to Babel, and add the es2015 transform plugin:

Step 1:

Add your test environment to .babelrc in the root of your project:

{
  "env": {
    "test": {
      "plugins": ["@babel/plugin-transform-modules-commonjs"]
    }
  }
}

Step 2:

Install the es2015 transform plugin:

npm install --save-dev @babel/plugin-transform-modules-commonjs

And that's it. Jest will enable compilation from ES modules to CommonJS automatically, without having to inform additional options to your jest property inside package.json.

edited Sep 16 '19 at 10:12

answered Apr 04 '18 at 17:09

Paulo Coghi

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2

this answer may be outdated, GarouDan's answer is the [officially suggested solution](https://jestjs.io/docs/en/getting-started#using-babel) – chantey Aug 16 '20 at 05:10
GarouDan's answer is not the officially suggested solution for ES6 modules but, instead, for Typescript scenarios. They are not the same thing. – Paulo Coghi Sep 22 '20 at 20:56
While GarouDan's solution includes typescript support, following the link I provided shows the well documented Jest ES6 implementation without typescript, from which GarouDan's solution is derived. The changes needed to support typescript are negligible, but I agree it is not relevent to the question. – chantey Sep 23 '20 at 21:18

score 3 · Answer 2 · answered Jul 29 '19 at 02:15

The solutions above didn't work for me. I was able to solve with this:

yarn add --dev babel-jest @babel/core @babel/preset-env @babel/preset-typescript

babel.config.js

module.exports = {
    presets: [
        [
            '@babel/preset-env',
            {
                targets: {
                    node: 'current',
                },
            },
        ],
        '@babel/preset-typescript'
    ],
};

where I'm using typescript.

Reference.

Test ES6 modules with Jest

2 Answers2

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