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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
  }
}

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

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

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-done-callback	Avoid 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-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-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

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

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