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Description

ESLint plugin for Jest

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eslint-plugin-jest

ESLint plugin for Jest

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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

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 | | fixable | | expect-expect | Enforce assertion to be made in a test body | recommended | | | lowercase-name | Enforce lowercase test names | | fixable | | 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-expect-assertions | Suggest using
expect.assertions()
OR
expect.hasAssertions()
| | suggest | | prefer-hooks-on-top | Suggest having hooks before any test cases | | | | prefer-spy-on | Suggest using
jest.spyOn()
| | fixable | | prefer-strict-equal | Suggest using
toStrictEqual()
| | suggest | | prefer-to-be-null | Suggest using
toBeNull()
| style | fixable | | prefer-to-be-undefined | Suggest using
toBeUndefined()
| 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-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 | recommended | | | valid-expect | Enforce valid
expect()
usage | recommended | | | valid-expect-in-promise | Enforce having return statement when testing with promises | 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

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