eslint-plugin-jest

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.

README

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

Add jest to the plugins section of your .eslintrc configuration file. You can omit the eslint-plugin- prefix:

{
  "plugins": ["jest"]
}

Then configure the rules you want to use under the rules section.

{
  "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"
  }
}

You can also tell ESLint about the environment variables provided by Jest by doing:

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

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

This setting is detected automatically based off the version of the jest package installed in node_modules, but it can also be provided explicitly if desired:

{
  "settings": {
    "jest": {
      "version": 26
    }
  }
}

Shareable configurations

Recommended

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

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

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

See ESLint documentation for more information about extending configuration files.

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"]
}

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

Rule	Description	Configurations	Fixable
consistent-test-it	Have control over test and it usages
expect-expect	Enforce assertion to be made in a test body
lowercase-name	Enforce lowercase test names
no-alias-methods	Disallow alias methods
no-commented-out-tests	Disallow commented out tests
no-conditional-expect	Prevent calling expect conditionally
no-deprecated-functions	Disallow use of deprecated functions
no-disabled-tests	Disallow disabled tests
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-if	Disallow conditional logic
no-interpolation-in-snapshots	Disallow string interpolation inside snapshots
no-jasmine-globals	Disallow Jasmine globals
no-jest-import	Disallow importing Jest
no-large-snapshots	disallow large snapshots
no-mocks-import	Disallow manually importing from __mocks__
no-restricted-matchers	Disallow specific matchers & modifiers
no-standalone-expect	Disallow using expect outside of it or test blocks
no-test-callback	Avoid using a callback in asynchronous tests
no-test-prefixes	Use .only and .skip over f and x
no-test-return-statement	Disallow explicitly returning from tests
prefer-called-with	Suggest using toBeCalledWith() or toHaveBeenCalledWith()
prefer-expect-assertions	Suggest using expect.assertions() OR expect.hasAssertions()
prefer-hooks-on-top	Suggest having hooks before any test cases
prefer-spy-on	Suggest using jest.spyOn()
prefer-strict-equal	Suggest using toStrictEqual()
prefer-to-be-null	Suggest using toBeNull()
prefer-to-be-undefined	Suggest using toBeUndefined()
prefer-to-contain	Suggest using toContain()
prefer-to-have-length	Suggest using toHaveLength()
prefer-todo	Suggest using test.todo
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	Enforce valid describe() callback
valid-expect	Enforce valid expect() usage
valid-expect-in-promise	Enforce having return statement when testing with promises
valid-title	Enforce valid titles

Credit

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

Related Projects

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

Changelog

23.20.0 (2020-07-30)

Features

• no-large-snapshots: deprecate whitelistedSnapshots for new name (#632) (706f5c2)