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.

Aliased Jest globals

You can tell this plugin about any global Jests you have aliased using the globalAliases setting:

{
  "settings": {
    "jest": {
      "globalAliases": {
        "describe": ["context"],
        "fdescribe": ["fcontext"],
        "xdescribe": ["xcontext"]
      }
    }
  }
}

Running rules only on test-related files

The rules provided by this plugin assume that the files they are checking are test-related. This means it's generally not suitable to include them in your top-level configuration as that applies to all files being linted which can include source files.

You can use overrides to have ESLint apply additional rules to specific files:

{
  "extends": ["eslint:recommended"],
  "overrides": [
    {
      "files": ["test/**"],
      "plugins": ["jest"],
      "extends": ["plugin:jest/recommended"],
      "rules": { "jest/prefer-expect-assertions": "off" }
    }
  ],
  "rules": {
    "indent": ["error", 2]
  }
}

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:

{
  "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:

module.exports = {
  settings: {
    jest: {
      version: require('jest/package.json').version,
    },
  },
};

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
max-nested-describe	Enforces a maximum depth to nested describe calls
no-alias-methods	Disallow alias methods
no-commented-out-tests	Disallow commented out tests
no-conditional-expect	Prevent calling `expect` conditionally
no-conditional-in-test	Disallow conditional logic in tests
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-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-comparison-matcher	Suggest using the built-in comparison matchers
prefer-equality-matcher	Suggest using the built-in equality matchers
prefer-expect-assertions	Suggest using `expect.assertions()` OR `expect.hasAssertions()`
prefer-expect-resolves	Prefer `await expect(...).resolves` over `expect(await ...)` syntax
prefer-hooks-in-order	Prefer having hooks in a consistent order
prefer-hooks-on-top	Suggest having hooks before any test cases
prefer-lowercase-title	Enforce lowercase test names
prefer-snapshot-hint	Prefer including a hint with external snapshots
prefer-spy-on	Suggest using `jest.spyOn()`
prefer-strict-equal	Suggest using `toStrictEqual()`
prefer-to-be	Suggest using `toBe()` for primitive literals
prefer-to-contain	Suggest using `toContain()`
prefer-to-have-length	Suggest using `toHaveLength()`
prefer-todo	Suggest using `test.todo`
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
valid-expect	Enforce valid `expect()` usage
valid-expect-in-promise	Ensure promises that have expectations in their chain are valid
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 it's 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	Enforce unbound methods are called with their expected scope

Credit

eslint-plugin-mocha
eslint-plugin-jasmine

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