eslint-plugin-jest

ESLint plugin for Jest

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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

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

json { "plugins": ["jest"] }

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

json { "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:

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

This is included in all configs shared by this plugin, so can be omitted if extending them.

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:

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

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:

json { "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:

json { "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:

json { "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 | | fixable | | expect-expect | Enforce assertion to be made in a test body | recommended | | | max-nested-describe | Enforces a maximum depth to nested describe calls | | | | no-alias-methods | Disallow alias methods | style | fixable | | no-commented-out-tests | Disallow commented out tests | recommended | | | no-conditional-expect | Prevent calling expect conditionally | recommended | | | no-deprecated-functions | Disallow use of deprecated functions | recommended | fixable | | no-disabled-tests | Disallow disabled tests | recommended | | | no-done-callback | Avoid using a callback in asynchronous tests and hooks | recommended | suggest | | no-duplicate-hooks | Disallow duplicate setup and teardown hooks | | | | no-export | Disallow using exports in files containing tests | recommended | | | no-focused-tests | Disallow focused tests | recommended | suggest | | no-hooks | Disallow setup and teardown hooks | | | | no-identical-title | Disallow identical titles | recommended | | | no-if | Disallow conditional logic | | | | no-interpolation-in-snapshots | Disallow string interpolation inside snapshots | recommended | | | no-jasmine-globals | Disallow Jasmine globals | recommended | fixable | | no-jest-import | Disallow importing Jest | recommended | | | no-large-snapshots | disallow large snapshots | | | | no-mocks-import | Disallow manually importing from __mocks__ | recommended | | | no-restricted-matchers | Disallow specific matchers & modifiers | | | | no-standalone-expect | Disallow using expect outside of it or test blocks | recommended | | | no-test-prefixes | Use .only and .skip over f and x | recommended | fixable | | no-test-return-statement | Disallow explicitly returning from tests | | | | prefer-called-with | Suggest using toBeCalledWith() or toHaveBeenCalledWith() | | | | prefer-comparison-matcher | Suggest using the built-in comparison matchers | | fixable | | prefer-equality-matcher | Suggest using the built-in equality matchers | | suggest | | prefer-expect-assertions | Suggest using expect.assertions() OR expect.hasAssertions() | | suggest | | prefer-expect-resolves | Prefer await expect(...).resolves over expect(await ...) syntax | | fixable | | prefer-hooks-on-top | Suggest having hooks before any test cases | | | | prefer-lowercase-title | Enforce lowercase test names | | fixable | | prefer-spy-on | Suggest using jest.spyOn() | | fixable | | prefer-strict-equal | Suggest using toStrictEqual() | | suggest | | prefer-to-be | Suggest using toBe() for primitive literals | style | fixable | | prefer-to-contain | Suggest using toContain() | style | fixable | | prefer-to-have-length | Suggest using toHaveLength() | style | fixable | | prefer-todo | Suggest using test.todo | | fixable | | 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 | recommended | | | valid-expect | Enforce valid expect() usage | recommended | | | valid-expect-in-promise | Ensure promises that have expectations in their chain are valid | recommended | | | valid-title | Enforce valid titles | recommended | fixable |

TypeScript Rules

In addition to the above rules, this plugin also includes a few advanced rules that are powered by type-checking information provided by TypeScript.

In order to use these rules, 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 its 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.

| Rule | Description | Configurations | Fixable | | ---------------------------------------------- | ------------------------------------------------------------- | -------------- | ------- | | unbound-method | Enforces unbound methods are called with their expected scope | | |

Credit

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

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