What is eslint-plugin-jest?
The eslint-plugin-jest package is an ESLint plugin that provides linting rules for Jest, a popular JavaScript testing framework. It helps maintain code quality and enforce best practices by analyzing test files for common issues and stylistic preferences.
What are eslint-plugin-jest's main functionalities?
Enforcing consistent test descriptions
This rule enforces a consistent test function name, either `test` or `it`, within the test files.
/* eslint jest/consistent-test-it: ["error", { fn: "test" }] */
// Incorrect
describe('myFeature', () => {
it('does something', () => {
// test implementation
});
});
// Correct
describe('myFeature', () => {
test('does something', () => {
// test implementation
});
});
Preventing disabled tests
This rule prevents the use of `xdescribe`, `xit`, or `test.skip`, which are used to disable tests, to ensure that all tests are run.
/* eslint jest/no-disabled-tests: "error" */
// Incorrect
xdescribe('myFeature', () => {
test('does something', () => {});
});
xit('does something', () => {});
// Correct
describe('myFeature', () => {
test('does something', () => {});
});
Ensuring tests contain assertions
This rule ensures that test blocks contain at least one assertion call, which is necessary for a meaningful test.
/* eslint jest/expect-expect: "error" */
// Incorrect
test('does something', () => {
// no assertions
});
// Correct
test('does something', () => {
expect(something).toBe(true);
});
Disallowing identical titles
This rule disallows using the same title for multiple test cases or `describe` blocks, which can cause confusion when trying to identify tests.
/* eslint jest/no-identical-title: "error" */
// Incorrect
describe('myFeature', () => {
test('does something', () => {});
test('does something', () => {});
});
// Correct
describe('myFeature', () => {
test('does something', () => {});
test('does something else', () => {});
});
Other packages similar to eslint-plugin-jest
eslint-plugin-mocha
This package provides linting rules for Mocha, another JavaScript test framework. It is similar to eslint-plugin-jest but tailored for Mocha's API and conventions.
eslint-plugin-jasmine
This package offers linting rules for Jasmine, a behavior-driven development framework for testing JavaScript code. It serves a similar purpose to eslint-plugin-jest but is specific to Jasmine's syntax and style.
eslint-plugin-testing-library
This ESLint plugin enforces best practices for the Testing Library, which is often used with Jest for testing React components. It complements eslint-plugin-jest by focusing on the specific patterns and practices of the Testing Library.
eslint-plugin-cypress
This plugin provides linting rules for Cypress, an end-to-end testing framework. While it is not specific to Jest, it offers similar functionality for maintaining code quality in a different testing context.
eslint-plugin-jest
ESLint plugin for Jest
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 = [
{
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',
},
},
{
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.
Recommended
This plugin exports a recommended configuration that enforces good testing
practices.
To enable this configuration with .eslintrc
, use the extends
property:
{
"extends": ["plugin:jest/recommended"]
}
To enable this configuration with eslint.config.js
, use
jest.configs['flat/recommended']
:
const jest = require('eslint-plugin-jest');
module.exports = [
{
files: [
],
...jest.configs['flat/recommended'],
},
];
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: [
],
...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: [
],
...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
πΌ
Configurations
enabled in.
β οΈ Configurations
set to warn in.
β
Set in the recommended
configuration.
π¨
Set in the style
configuration.
π§
Automatically fixable by the
--fix
CLI option.
π‘
Manually fixable by
editor suggestions.
Requires Type Checking
NameΒ Β Β Β Β Β Β Β Β Β | Description | πΌ | β οΈ | π§ | π‘ |
---|
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
Related Projects
eslint-plugin-jest-extended
This is a sister plugin to eslint-plugin-jest
that provides support for the
matchers provided by
jest-extended
.
https://github.com/jest-community/eslint-plugin-jest-extended
eslint-plugin-jest-formatting
This project aims to provide formatting rules (auto-fixable where possible) to
ensure consistency and readability in jest test suites.
https://github.com/dangreenisrael/eslint-plugin-jest-formatting
eslint-plugin-istanbul
A set of rules to enforce good practices for Istanbul, one of the code coverage
tools used by Jest.
https://github.com/istanbuljs/eslint-plugin-istanbul