eslint-plugin-jest

v28.10.0

Published

11 days ago

ESLint rules for Jest

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eslint eslintplugin eslint-plugin

Installation

yarn add --dev eslint eslint-plugin-jest

Note: If you installed ESLint globally then you must also install eslint-plugin-jest globally.

Usage

If you're using flat configuration:

With flat configuration, just import the plugin and away you go:

const pluginJest = require('eslint-plugin-jest');

module.exports = [
  {
    // update this to match your test files
    files: ['**/*.spec.js', '**/*.test.js'],
    plugins: { jest: pluginJest },
    languageOptions: {
      globals: pluginJest.environments.globals.globals,
    },
    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',
    },
  },
];

With legacy configuration, add jest to the plugins section of your .eslintrc configuration file. You can omit the eslint-plugin- prefix:

{
  "plugins": ["jest"],
  "env": {
    "jest/globals": true
  },
  "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"
  }
}

[!NOTE]
You only need to explicitly include our globals if you're not using one of our shared configs

Aliased Jest globals

You can tell this plugin about any global Jests you have aliased using the globalAliases setting:

{
  "settings": {
    "jest": {
      "globalAliases": {
        "describe": ["context"],
        "fdescribe": ["fcontext"],
        "xdescribe": ["xcontext"]
      }
    }
  }
}

Aliased `@jest/globals`

You can tell this plugin to treat a different package as the source of Jest globals using the globalPackage setting:

{
  "settings": {
    "jest": {
      "globalPackage": "bun:test"
    }
  }
}

[!WARNING]
While this can be used to apply rules when using alternative testing libraries and frameworks like bun, vitest and node, there's no guarantee the semantics this plugin assumes will hold outside of Jest

Running rules only on test-related files

The rules provided by this plugin assume that the files they are checking are test-related. This means it's generally not suitable to include them in your top-level configuration as that applies to all files being linted which can include source files.

For .eslintrc configs you can use overrides to have ESLint apply additional rules to specific files:

{
  "extends": ["eslint:recommended"],
  "overrides": [
    {
      "files": ["test/**"],
      "plugins": ["jest"],
      "extends": ["plugin:jest/recommended"],
      "rules": { "jest/prefer-expect-assertions": "off" }
    }
  ],
  "rules": {
    "indent": ["error", 2]
  }
}

For eslint.config.js you can use files and ignores:

const jest = require('eslint-plugin-jest');

module.exports = [
  ...require('@eslint/js').configs.recommended,
  {
    files: ['test/**'],
    ...jest.configs['flat/recommended'],
    rules: {
      ...jest.configs['flat/recommended'].rules,
      'jest/prefer-expect-assertions': 'off',
    },
  },
  // you can also configure jest rules in other objects, so long as some of the `files` match
  {
    files: ['test/**'],
    rules: { 'jest/prefer-expect-assertions': 'off' },
  },
];

Jest `version` setting

The behaviour of some rules (specifically no-deprecated-functions) change depending on the version of Jest being used.

By default, this plugin will attempt to determine to locate Jest using require.resolve, meaning it will start looking in the closest node_modules folder to the file being linted and work its way up.

Since we cache the automatically determined version, if you're linting sub-folders that have different versions of Jest, you may find that the wrong version of Jest is considered when linting. You can work around this by providing the Jest version explicitly in nested ESLint configs:

{
  "settings": {
    "jest": {
      "version": 27
    }
  }
}

To avoid hard-coding a number, you can also fetch it from the installed version of Jest if you use a JavaScript config file such as .eslintrc.js:

module.exports = {
  settings: {
    jest: {
      version: require('jest/package.json').version,
    },
  },
};

Shareable configurations

[!NOTE]
eslint.config.js compatible versions of configs are available prefixed with flat/ and may be subject to small breaking changes while ESLint v9 is being finalized.

Style

This plugin also exports a configuration named style, which adds some stylistic rules, such as prefer-to-be-null, which enforces usage of toBeNull over toBe(null).

To enable this configuration use the extends property in your .eslintrc config file:

{
  "extends": ["plugin:jest/style"]
}

To enable this configuration with eslint.config.js, use jest.configs['flat/style']:

const jest = require('eslint-plugin-jest');

module.exports = [
  {
    files: [
      /* glob matching your test files */
    ],
    ...jest.configs['flat/style'],
  },
];

All

If you want to enable all rules instead of only some you can do so by adding the all configuration to your .eslintrc config file:

{
  "extends": ["plugin:jest/all"]
}

To enable this configuration with eslint.config.js, use jest.configs['flat/all']:

const jest = require('eslint-plugin-jest');

module.exports = [
  {
    files: [
      /* glob matching your test files */
    ],
    ...jest.configs['flat/all'],
  },
];

While the recommended and style configurations only change in major versions the all configuration may change in any release and is thus unsuited for installations requiring long-term consistency.

Rules

💼 Configurations enabled in.
⚠️ Configurations set to warn in.
✅ Set in the recommended configuration.
🎨 Set in the style configuration.
🔧 Automatically fixable by the --fix CLI option.
💡 Manually fixable by editor suggestions.

Requires Type Checking

| Name | Description | 💼 | ⚠️ | 🔧 | 💡 | | :--------------------------------------------- | :----------------------------------------------------------- | :-- | :-- | :-- | :-- | | unbound-method | Enforce unbound methods are called with their expected scope | | | | |

In order to use the rules powered by TypeScript type-checking, you must be using @typescript-eslint/parser & adjust your eslint config as outlined here.

Note that unlike the type-checking rules in @typescript-eslint/eslint-plugin, the rules here will fallback to doing nothing if type information is not available, meaning it's safe to include them in shared configs that could be used on JavaScript and TypeScript projects.

Also note that unbound-method depends on @typescript-eslint/eslint-plugin, as it extends the original unbound-method rule from that plugin.

Credit

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