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/valid-expect": "error"
  }
}

You can also whitelist the environment variables provided by Jest by doing:

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

Supported Rules

• no-disabled-tests - disallow disabled tests.
• no-focused-tests - disallow focused tests.
• no-identical-title - disallow identical titles.
• valid-expect - ensure expect is called correctly.

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"]
}

See ESLint documentation for more information about extending configuration files.

The rules enabled in this configuration are:

• jest/no-disabled-tests
• jest/no-focused-tests
• jest/no-identical-title
• jest/valid-expect

Credit

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