How to use ESLint with Jest

Question

I'm attempting to use the ESLint linter with the Jest testing framework.

Jest tests run with some globals like jest, which I'll need to tell the linter about; but the tricky thing is the directory structure, with Jest the tests are embedded with the source code in __tests__ folders, so the directory structure looks something like:

src
    foo
        foo.js
        __tests__
            fooTest.js
    bar
        bar.js
        __tests__
            barTest.js

Normally, I'd have all my tests under a single dir, and I could just add an .eslintrc file there to add the globals... but I certainly don't want to add a .eslintrc file to every single __test__ dir.

For now, I've just added the test globals to the global .eslintrc file, but since that means I could now reference jest in non-testing code, that doesn't seem like the "right" solution.

Is there a way to get eslint to apply rules based on some pattern based on the directory name, or something like that?

Ceilometer

This is a bit too brute force for an actual answer, but you could have a separate linting task that manually uses aneslint-test file with a glob, e.g. eslint **/__tests__/*.js -c eslint-test.yml. That said, I don't think there's much danger of a jest or beforeEach global leaking out into production code ;) – Carma

Answer 1

The docs show you are now able to add:

"env": {
    "jest/globals": true
}

To your .eslintrc which will add all the jest related things to your environment, eliminating the linter errors/warnings.

You may need to include plugins: ["jest"] to your esconfig, and add the eslint-plugin-jest plugin if it still isn't working.

Entrammel

With this method the usage of "describe" or "it" outside of files that match the ".test.js" or "__tests__/.js" pattern will not result in linting errors. Is there any way to achieve this? – Fireproof

@l0rin you could add a .eslintrc file that extend you default .eslintrc in your __tests__ folder. If you have same problem as OP (multiple test folders), then you can generate those .eslintrc with a template and a tiny bash script (something likels **/__tests/ | xargs cp templates/.eslintrc) – Bodyguard

related link here – Hogan

Is this still accurate? The docs specifically say "jest/globals": true rather than "jest": true. – Gorgon

@Sawtaytoes good spot. I have updated the answer accordingly :) – Entrammel

To be clear, you have to include plugins": ["jest"] to your esconfig, and add the eslint-plugin-jest plugin. – Astomatous

Answer 2

ESLint supports this as of version >= 4:

/*
.eslintrc.js
*/
const ERROR = 2;
const WARN = 1;

module.exports = {
  extends: "eslint:recommended",
  env: {
    es6: true
  },
  overrides: [
    {
      files: [
        "**/*.test.js"
      ],
      env: {
        jest: true // now **/*.test.js files' env has both es6 *and* jest
      },
      // Can't extend in overrides: https://github.com/eslint/eslint/issues/8813
      // "extends": ["plugin:jest/recommended"]
      plugins: ["jest"],
      rules: {
        "jest/no-disabled-tests": "warn",
        "jest/no-focused-tests": "error",
        "jest/no-identical-title": "error",
        "jest/prefer-to-have-length": "warn",
        "jest/valid-expect": "error"
      }
    }
  ],
};

Here is a workaround (from another answer on here, vote it up!) for the "extend in overrides" limitation of eslint config :

overrides: [
  Object.assign(
    {
      files: [ '**/*.test.js' ],
      env: { jest: true },
      plugins: [ 'jest' ],
    },
    require('eslint-plugin-jest').configs.recommended
  )
]

From https://github.com/eslint/eslint/issues/8813#issuecomment-320448724

Semaphore

Thank you, this is totally the right solution for this question, as it actually answers it. worked for me! – Skewer

This is great! With updating my ESLint to version >= 4 and adding a "files" and "env" object to "overrides" in eslint.rc I no longer have to worry about Jest specific syntax passing linting outside of the testing files. – Fantasm

Excellent solution and also works for other frameworks (jasmine) when you have a non-standard folder structure. – Toner

I'm the guy who wrote the accepted answer - this answer is much better than mine! Although at the time I wrote my answer, it was the only way to solve this problem well. – Entrammel

ESLint now supports extending in overrides – Pandolfi

Answer 3

You can also set the test env in your test file as follows:

/* eslint-env jest */

describe(() => {
  /* ... */
})

Dispensatory

Answer 4

To complete Zachary's answer, here is a workaround for the "extend in overrides" limitation of eslint config :

overrides: [
  Object.assign(
    {
      files: [ '**/*.test.js' ],
      env: { jest: true },
      plugins: [ 'jest' ],
    },
    require('eslint-plugin-jest').configs.recommended
  )
]

From https://github.com/eslint/eslint/issues/8813#issuecomment-320448724

Abductor

Answer 5

As of 2021, I think the correct way or at least the one that works is to install @types/jest and eslint-plugin-jest:

npm i -D eslint-plugin-jest @types/jest

And adding the Jest plugin into .eslintrc.js with the overrides instruction mentioned by @Loren:

module.exports = {
  ...
  plugins: ["jest"],
  ...
  overrides: [
    {
      files: ["**/*.test.js"],
      env: { "jest/globals": true },
      plugins: ["jest"],
      extends: ["plugin:jest/recommended"],
    },
  ],
  ...
};

This way you get linting errors in your source files as well as in test files, but in test files you don't get linting errors for test and other Jest's functions, but you will get them in your source files as they will appear as undefined there.

Feder

Many solutions purposed to put "jest/globals": true but it seems to make Eslint to stop working properly in other js files. But this solution is working flawlessly for me. It allows eslint to lint .test and .js files properly. – Beedon

you can update a file rule to "**/*.test.[j|t]s" – Castigate

Answer 6

I solved the problem REF

Run

# For Yarn
yarn add eslint-plugin-jest -D

# For NPM
npm i eslint-plugin-jest -D

And then add in your .eslintrc file

{
    "extends": ["airbnb","plugin:jest/recommended"],
}

Mendenhall

Answer 7

First install eslint-plugin-jest

Running:

yarn add eslint-plugin-jest

or

npm install eslint-plugin-jest

Then edit .eslintrc.json

{
   "env":{
     "jest": true
   }
}

Loading

Answer 8

Add environment only for __tests__ folder

You could add a .eslintrc.yml file in your __tests__ folders, that extends you basic configuration:

extends: <relative_path to .eslintrc>
env:
    jest: true

If you have only one __tests__folder, this solution is the best since it scope jest environment only where it is needed.

Dealing with many test folders

If you have more test folders (OPs case), I'd still suggest to add those files. And if you have tons of those folders can add them with a simple zsh script:

#!/usr/bin/env zsh

for folder in **/__tests__/ ;do
    count=$(($(tr -cd '/' <<< $folder | wc -c)))
    echo $folder : $count
    cat <<EOF > $folder.eslintrc.yml
extends: $(printf '../%.0s' {1..$count}).eslintrc
env:
    jest: true
EOF
done

This script will look for __tests__ folders and add a .eslintrc.yml file with to configuration shown above. This script has to be launched within the folder containing your parent .eslintrc.

Bodyguard

.eslintrc.yml to set second folder to be listed, super nice! To stop indexing it and avoid error messages, you can also set "ignorePatterns": ["tests/*"] in eslintrc file – Infamous

Answer 9

some of the answers assume you have eslint-plugin-jest installed, however without needing to do that, you can simply do this in your .eslintrc file, add:

  "globals": {
    "jest": true,
  }

Lasting

Thanks - this worked - this comment needs more votes. – Protagoras

Answer 10

As of ESLint V 6 (released in late 2019), you can use extends in the glob based config as follows:

    "overrides": [
      {
        "files": ["*.test.js"],
        "env": {
          "jest": true
        },
        "plugins": ["jest"],
        "extends": ["plugin:jest/recommended"]
      }
    ]

Vituperation

Answer 11

Pattern based configs are scheduled for 2.0.0 release of ESLint. For now, however, you will have to create two separate tasks (as mentioned in the comments). One for tests and one for the rest of the code and run both of them, while providing different .eslintrc files.

P.S. There's a jest environment coming in the next release of ESLint, it will register all of the necessary globals.

Picaresque

Answer 12

I got it running after spending some time trying out different options. Hope this helps anyone else getting stuck.

.eslintrc.json (in root project folder):

{
    "env": {
        "browser": true,
        "es2021": true,
        "jest/globals": true
    },
    "extends": [
        "standard",
        "plugin:jest/all"
    ],
    "parser": "@babel/eslint-parser",
    "parserOptions": {
        "ecmaVersion": 12,
        "sourceType": "module"
    },
    "rules": {
        "jest/no-hooks": [
            "error",
            {
                "allow": [
                    "afterEach",
                    "beforeEach"
                ]
            }
        ]
    },
    "plugins": [
        "jest"
    ]
}

Empty .babelrc (in root project folder):

{}

.package.json (in root project folder):

{
  "scripts": {
    "test": "jest",
    "lint": "npx eslint --format=table .",
    "lintfix": "npx eslint --fix ."
  },
  "devDependencies": {
    "@babel/core": "^7.15.0",
    "@babel/eslint-parser": "^7.15.0",
    "aws-sdk-mock": "^5.2.1",
    "eslint": "^7.32.0",
    "eslint-config-standard": "^16.0.3",
    "eslint-plugin-import": "^2.24.0",
    "eslint-plugin-jest": "^24.4.0",
    "eslint-plugin-node": "^11.1.0",
    "eslint-plugin-promise": "^5.1.0",
    "jest": "^27.0.6"
  }
}

VS Code settings.xml (editor configuration: enables auto fix on save + babel parser):

    "eslint.alwaysShowStatus": true,
    "eslint.format.enable": true,
    "eslint.lintTask.enable": true,
    "eslint.options": {
        "parser": "@babel/eslint-parser"
    },
    "editor.codeActionsOnSave": {
        "source.fixAll.eslint": true
    },
    "eslint.validate": [
        "javascript"
    ]

Incursive

Answer 13

In your .eslintignore file add the following value:

**/__tests__/

This should ignore all instances of the __tests__ directory and their children.

Gisela

That's not quite what I want, I don't want to ignore the test files, I still want to lint them, I just want to figure out how to specify the necessary options to lint them correctly. – Ceilometer

Very bad idea, eslint helps in all code - including test code. – Ronaldronalda