eslint-plugin-jest

ESLint plugin for Jest


Installation

``bash
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:

`js
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:

`json
{
"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:

`json
{
"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:

`json
{
"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

$3

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:

`json
{
"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:

`js
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' },
},
];
`

$3

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:

`json
{
"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:

`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.

$3

This plugin exports a recommended configuration that enforces good testing
practices.

To enable this configuration with .eslintrc, use the extends property:

`json
{
"extends": ["plugin:jest/recommended"]
}
`

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

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

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

$3

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:

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

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

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

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

$3

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:

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

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

`js
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.

| Name                              | Description | 💼 | ⚠️ | 🔧 | 💡 |
| :----------------------------------------------------------------------------------- | :------------------------------------------------------------------------ | :-- | :-- | :-- | :-- |
| consistent-test-it | Enforce test and it usage conventions | | | 🔧 | |
| expect-expect | Enforce assertion to be made in a test body | | ✅ | | |
| max-expects | Enforces a maximum number assertion calls in a test body | | | | |
| max-nested-describe | Enforces a maximum depth to nested describe calls | | | | |
| no-alias-methods | Disallow alias methods | ✅ | | 🔧 | |
| no-commented-out-tests | Disallow commented out tests | | ✅ | | |
| no-conditional-expect | Disallow calling expect conditionally | ✅ | | | |
| no-conditional-in-test | Disallow conditional logic in tests | | | | |
| no-confusing-set-timeout | Disallow confusing usages of jest.setTimeout | | | | |
| no-deprecated-functions | Disallow use of deprecated functions | ✅ | | 🔧 | |
| no-disabled-tests | Disallow disabled tests | | ✅ | | |
| no-done-callback | Disallow using a callback in asynchronous tests and hooks | ✅ | | | 💡 |
| no-duplicate-hooks | Disallow duplicate setup and teardown hooks | | | | |
| no-export | Disallow using exports in files containing tests | ✅ | | | |
| no-focused-tests | Disallow focused tests | ✅ | | | 💡 |
| no-hooks | Disallow setup and teardown hooks | | | | |
| no-identical-title | Disallow identical titles | ✅ | | | |
| no-interpolation-in-snapshots | Disallow string interpolation inside snapshots | ✅ | | | |
| no-jasmine-globals | Disallow Jasmine globals | ✅ | | 🔧 | |
| no-large-snapshots | Disallow large snapshots | | | | |
| no-mocks-import | Disallow manually importing from __mocks__ | ✅ | | | |
| no-restricted-jest-methods | Disallow specific jest. methods | | | | |
| no-restricted-matchers | Disallow specific matchers & modifiers | | | | |
| no-standalone-expect | Disallow using expect outside of it or test blocks | ✅ | | | |
| no-test-prefixes | Require using .only and .skip over f and x | ✅ | | 🔧 | |
| no-test-return-statement | Disallow explicitly returning from tests | | | | |
| no-unneeded-async-expect-function | Disallow unnecessary async function wrapper for expected promises | | | 🔧 | |
| no-untyped-mock-factory | Disallow using jest.mock() factories without an explicit type parameter | | | 🔧 | |
| padding-around-after-all-blocks | Enforce padding around afterAll blocks | | | 🔧 | |
| padding-around-after-each-blocks | Enforce padding around afterEach blocks | | | 🔧 | |
| padding-around-all | Enforce padding around Jest functions | | | 🔧 | |
| padding-around-before-all-blocks | Enforce padding around beforeAll blocks | | | 🔧 | |
| padding-around-before-each-blocks | Enforce padding around beforeEach blocks | | | 🔧 | |
| padding-around-describe-blocks | Enforce padding around describe blocks | | | 🔧 | |
| padding-around-expect-groups | Enforce padding around expect groups | | | 🔧 | |
| padding-around-test-blocks | Enforce padding around test and it blocks | | | 🔧 | |
| prefer-called-with | Suggest using toHaveBeenCalledWith() | | | | |
| prefer-comparison-matcher | Suggest using the built-in comparison matchers | | | 🔧 | |
| prefer-each | Prefer using .each rather than manual loops | | | | |
| prefer-ending-with-an-expect | Prefer having the last statement in a test be an assertion | | | | |
| prefer-equality-matcher | Suggest using the built-in equality matchers | | | | 💡 |
| prefer-expect-assertions | Suggest using expect.assertions() OR expect.hasAssertions() | | | | 💡 |
| prefer-expect-resolves | Prefer await expect(...).resolves over expect(await ...) syntax | | | 🔧 | |
| prefer-hooks-in-order | Prefer having hooks in a consistent order | | | | |
| prefer-hooks-on-top | Suggest having hooks before any test cases | | | | |
| prefer-importing-jest-globals | Prefer importing Jest globals | | | 🔧 | |
| prefer-jest-mocked | Prefer jest.mocked() over fn as jest.Mock | | | 🔧 | |
| prefer-lowercase-title | Enforce lowercase test names | | | 🔧 | |
| prefer-mock-promise-shorthand | Prefer mock resolved/rejected shorthands for promises | | | 🔧 | |
| prefer-mock-return-shorthand | Prefer mock return shorthands | | | 🔧 | |
| prefer-snapshot-hint | Prefer including a hint with external snapshots | | | | |
| prefer-spy-on | Suggest using jest.spyOn() | | | 🔧 | |
| prefer-strict-equal | Suggest using toStrictEqual() | | | | 💡 |
| prefer-to-be | Suggest using toBe() for primitive literals | 🎨 | | 🔧 | |
| prefer-to-contain | Suggest using toContain() | 🎨 | | 🔧 | |
| prefer-to-have-been-called | Suggest using toHaveBeenCalled | | | 🔧 | |
| prefer-to-have-been-called-times | Suggest using toHaveBeenCalledTimes() | | | 🔧 | |
| prefer-to-have-length | Suggest using toHaveLength() | 🎨 | | 🔧 | |
| prefer-todo | Suggest using test.todo | | | 🔧 | |
| require-hook | Require setup and teardown code to be within a hook | | | | |
| require-to-throw-message | Require a message for toThrow() | | | | |
| require-top-level-describe | Require test cases and hooks to be inside a describe block | | | | |
| valid-describe-callback | Enforce valid describe() callback | ✅ | | | |
| valid-expect | Enforce valid expect() usage | ✅ | | 🔧 | |
| valid-expect-in-promise | Require promises that have expectations in their chain to be valid | ✅ | | | |
| valid-mock-module-path | Disallow mocking of non-existing module paths | | | | |
| valid-title | Enforce valid titles | ✅ | | 🔧 | |

$3

| Name                      | Description | 💼 | ⚠️ | 🔧 | 💡 |
| :------------------------------------------------------------------- | :------------------------------------------------------------------------------------------ | :-- | :-- | :-- | :-- |
| no-error-equal | Disallow using equality matchers on error types | | | | |
| no-unnecessary-assertion | Disallow unnecessary assertions based on types | | | | |
| unbound-method | Enforce unbound methods are called with their expected scope | | | | |
| valid-expect-with-promise | Require that resolve and reject modifiers are present (and only) for promise-like types | | | | |

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

- eslint-plugin-mocha
- eslint-plugin-jasmine

Related Projects

$3

This is a sister plugin to eslint-plugin-jest that provides support for the
matchers provided by
jest-extended.

$3

This project aims to provide formatting rules (auto-fixable where possible) to
ensure consistency and readability in jest test suites.

$3

A set of rules to enforce good practices for Istanbul, one of the code coverage
tools used by Jest.

[no-deprecated-functions`]: docs/rules/no-deprecated-functions.md