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Configuring Jest

The Jest philosophy is to work great by default, but sometimes you just need more configuration power.

It is recommended to define the configuration in a dedicated JavaScript, TypeScript or JSON file. The file will be discovered automatically, if it is named jest.config.js|ts|mjs|mts|cjs|cts|json. You can use --config flag to pass an explicit path to the file.

nota

Keep in mind that the resulting configuration object must always be JSON-serializable.

Open Config Examples
  • Using defineConfig from jest you should follow this:
jest.config.js
const {defineConfig} = require('jest');

module.exports = defineConfig({
  // ... Specify options here.
});
  • You can retrieve Jest's defaults from jest-config to extend them if needed:
jest.config.js
const {defineConfig} = require('jest');
const {defaults} = require('jest-config');

module.exports = defineConfig({
  moduleDirectories: [...defaults.moduleDirectories, 'bower_components'],
});
  • When using a separate Jest config, you can also extend Jest's options from another config file if needed using mergeConfig from jest:
jest.config.js
const {defineConfig, mergeConfig} = require('jest');
const jestConfig = require('./jest.config');

module.exports = mergeConfig(
  jestConfig,
  defineConfig({
    // ... Specify options here.
  }),
);
  • If your Jest config needs to be defined as a function, you can define the config like this:
jest.config.js
const {defineConfig, mergeConfig} = require('jest');
const jestConfig = require('./jest.config');

module.exports = defineConfig(() =>
  mergeConfig(
    jestConfig,
    defineConfig({
      // ... Specify options here.
    }),
  ),
);
  • The configuration also can be stored in a JSON file as a plain object:
jest.config.json
{
  "bail": 1,
  "verbose": true
}
  • Alternatively Jest's configuration can be defined through the "jest" key in the package.json of your project:
package.json
{
  "name": "my-project",
  "jest": {
    "verbose": true
  }
}
  • Also Jest's configuration json file can be referenced through the "jest" key in the package.json of your project:
package.json
{
  "name": "my-project",
  "jest": "./path/to/config.json"
}
consejo

To read TypeScript configuration files Jest by default requires ts-node. You can override this behavior by adding a @jest-config-loader docblock at the top of the file. Currently, ts-node and esbuild-register is supported. Make sure ts-node or the loader you specify is installed.

jest.config.ts
/** @jest-config-loader ts-node */
// or
/** @jest-config-loader esbuild-register */

import {defineConfig} from 'jest';

export default defineConfig({
  verbose: true,
});

You can also pass options to the loader, for instance to enable transpileOnly.

jest.config.ts
/** @jest-config-loader ts-node */
/** @jest-config-loader-options {"transpileOnly": true} */

import type {defineConfig} from 'jest';

export default defineConfig({
  verbose: true,
});

Options​

Reference​

automock [boolean]​

Default: false

This option tells Jest that all imported modules in your tests should be mocked automatically. All modules used in your tests will have a replacement implementation, keeping the API surface.

Example:

utils.js
export default {
  authorize: () => 'token',
  isAuthorized: secret => secret === 'wizard',
};
__tests__/automock.test.js
import utils from '../utils';

test('if utils mocked automatically', () => {
  // Public methods of `utils` are now mock functions
  expect(utils.authorize.mock).toBeTruthy();
  expect(utils.isAuthorized.mock).toBeTruthy();

  // You can provide them with your own implementation
  // or pass the expected return value
  utils.authorize.mockReturnValue('mocked_token');
  utils.isAuthorized.mockReturnValue(true);

  expect(utils.authorize()).toBe('mocked_token');
  expect(utils.isAuthorized('not_wizard')).toBeTruthy();
});
nota

Node modules are automatically mocked when you have a manual mock in place (e.g.: __mocks__/lodash.js). More info here.

Node.js core modules, like fs, are not mocked by default. They can be mocked explicitly, like jest.mock('fs').

bail [number | boolean]​

Default: 0

By default, Jest runs all tests and produces all errors into the console upon completion. The bail config option can be used here to have Jest stop running tests after n failures. Setting bail to true is the same as setting bail to 1.

cacheDirectory [string]​

Default: "/tmp/<path>"

The directory where Jest should store its cached dependency information.

Jest attempts to scan your dependency tree once (up-front) and cache it in order to ease some of the filesystem churn that needs to happen while running tests. This config option lets you customize where Jest stores that cache data on disk.

clearMocks [boolean]​

Default: false

Automatically clear mock calls, instances, contexts and results before every test. Equivalent to calling jest.clearAllMocks() before each test. This does not remove any mock implementation that may have been provided.

collectCoverage [boolean]​

Default: false

Indicates whether the coverage information should be collected while executing the test. Because this retrofits all executed files with coverage collection statements, it may significantly slow down your tests.

Jest ships with two coverage providers: babel (default) and v8. See the coverageProvider option for more details.

información

The babel and v8 coverage providers use /* istanbul ignore next */ and /* c8 ignore next */ comments to exclude lines from coverage reports, respectively. For more information, you can view the istanbuljs documentation and the c8 documentation.

collectCoverageFrom [array]​

Default: undefined

An array of glob patterns indicating a set of files for which coverage information should be collected. If a file matches the specified glob pattern, coverage information will be collected for it even if no tests exist for this file and it's never required in the test suite.

jest.config.js
const {defineConfig} = require('jest');

module.exports = defineConfig({
  collectCoverageFrom: [
    '**/*.{js,jsx}',
    '!**/node_modules/**',
    '!**/vendor/**',
  ],
});

This will collect coverage information for all the files inside the project's rootDir, except the ones that match **/node_modules/** or **/vendor/**.

consejo

Each glob pattern is applied in the order they are specified in the config. For example ["!**/__tests__/**", "**/*.js"] will not exclude __tests__ because the negation is overwritten with the second pattern. In order to make the negated glob work in this example it has to come after **/*.js.

nota

This option requires collectCoverage to be set to true or Jest to be invoked with --coverage.

Help:

If you are seeing coverage output such as...

=============================== Coverage summary ===============================
Statements   : Unknown% ( 0/0 )
Branches     : Unknown% ( 0/0 )
Functions    : Unknown% ( 0/0 )
Lines        : Unknown% ( 0/0 )
================================================================================
Jest: Coverage data for global was not found.

Most likely your glob patterns are not matching any files. Refer to the micromatch documentation to ensure your globs are compatible.

coverageDirectory [string]​

Default: undefined

The directory where Jest should output its coverage files.

coveragePathIgnorePatterns [array<string>]​

Default: ["/node_modules/"]

An array of regexp pattern strings that are matched against all file paths before executing the test. If the file path matches any of the patterns, coverage information will be skipped.

These pattern strings match against the full path. Use the <rootDir> string token to include the path to your project's root directory to prevent it from accidentally ignoring all of your files in different environments that may have different root directories. Example: ["<rootDir>/build/", "<rootDir>/node_modules/"].

coverageProvider [string]​

Indicates which provider should be used to instrument code for coverage. Allowed values are babel (default) or v8.

coverageReporters [array<string | [string, options]>]​

Default: ["clover", "json", "lcov", "text"]

A list of reporter names that Jest uses when writing coverage reports. Any istanbul reporter can be used.

consejo

Setting this option overwrites the default values. Add "text" or "text-summary" to see a coverage summary in the console output.

Additional options can be passed using the tuple form. For example, you may hide coverage report lines for all fully-covered files:

jest.config.js
const {defineConfig} = require('jest');

module.exports = defineConfig({
  coverageReporters: ['clover', 'json', 'lcov', ['text', {skipFull: true}]],
});

For more information about the options object shape refer to CoverageReporterWithOptions type in the type definitions.

coverageThreshold [object]​

Default: undefined

This will be used to configure minimum threshold enforcement for coverage results. Thresholds can be specified as global, as a glob, and as a directory or file path. If thresholds aren't met, jest will fail.

  • If a threshold is set to a positive number, it will be interpreted as the minimum percentage of coverage required.

  • If a threshold is set to a negative number, it will be treated as the maximum number of uncovered items allowed.

For example, with the following configuration jest will fail if there is less than 80% branch, line, and function coverage, or if there are more than 10 uncovered statements:

jest.config.js
const {defineConfig} = require('jest');

module.exports = defineConfig({
  coverageThreshold: {
    global: {
      // Requires 80% branch coverage
      branches: 80,
      // Requires 80% function coverage
      functions: 80,
      // Requires 80% line coverage
      lines: 80,
      // Require that no more than 10 statements are uncovered
      statements: -10,
    },
  },
});

coverageThreshold.global.lines [number]​

Global threshold for lines.

coverageThreshold.global.functions [number]​

Global threshold for functions.

coverageThreshold.global.statements [number]​

Global threshold for statements.

coverageThreshold.global.branches [number]​

Global threshold for branches.

coverageThreshold[glob-pattern] [object]​

Default: undefined

Sets thresholds for files matching the glob pattern. This allows you to enforce a high global standard while also setting specific thresholds for critical files or directories.

información

When globs or paths are defined together with a global threshold, Jest applies each threshold independently — specific patterns use their own limits, while the global threshold applies to files not matched by any pattern. If all files are matched by path or glob patterns, the global threshold falls back to applying against all covered files.

If the file specified by path is not found, an error is returned.

jest.config.js
const {defineConfig} = require('jest');

module.exports = defineConfig({
  coverageThreshold: {
    global: {
      branches: 50,
      functions: 50,
      lines: 50,
      statements: 50,
    },
    './src/components/': {
      branches: 40,
      statements: 40,
    },
    './src/reducers/**/*.js': {
      statements: 90,
    },
    './src/api/very-important-module.js': {
      branches: 100,
      functions: 100,
      lines: 100,
      statements: 100,
    },
  },
});

Jest will fail if:

  • The ./src/components directory has less than 40% branch/statement coverage.
  • One of the files matching the ./src/reducers/**/*.js glob has less than 90% statement coverage.
  • The ./src/api/very-important-module.js file has less than 100% coverage.
  • All files that are not matched by ./src/components, ./src/reducers/**/*.js, or ./src/api/very-important-module.js have less than 50% coverage (global).

dependencyExtractor [string]​

Default: undefined

This option allows the use of a custom dependency extractor. It must be a node module that exports an object with an extract function. E.g.:

const crypto = require('crypto');
const fs = require('fs');

module.exports = {
  extract(code, filePath, defaultExtract) {
    const deps = defaultExtract(code, filePath);
    // Scan the file and add dependencies in `deps` (which is a `Set`)
    return deps;
  },
  getCacheKey() {
    return crypto
      .createHash('md5')
      .update(fs.readFileSync(__filename))
      .digest('hex');
  },
};

The extract function should return an iterable (Array, Set, etc.) with the dependencies found in the code.

That module can also contain a getCacheKey function to generate a cache key to determine if the logic has changed and any cached artifacts relying on it should be discarded.

displayName [string, object]​

default: undefined

Allows for a label to be printed alongside a test while it is running. This becomes more useful in multi-project repositories where there can be many jest configuration files. This visually tells which project a test belongs to.

jest.config.js
const {defineConfig} = require('jest');

module.exports = defineConfig({
  displayName: 'CLIENT',
});

Alternatively, an object with the properties name and color can be passed. This allows for a custom configuration of the background color of the displayName. displayName defaults to white when its value is a string. Jest uses chalk to provide the color. As such, all of the valid options for colors supported by chalk are also supported by Jest.

jest.config.js
const {defineConfig} = require('jest');

module.exports = defineConfig({
  displayName: {
    name: 'CLIENT',
    color: 'blue',
  },
});

errorOnDeprecated [boolean]​

Default: false

Make calling deprecated APIs throw helpful error messages. Useful for easing the upgrade process.

extensionsToTreatAsEsm [array<string>]​

Default: []

Jest will run .mjs and .js files with nearest package.json's type field set to module as ECMAScript Modules. If you have any other files that should run with native ESM, you need to specify their file extension here.

jest.config.js
const {defineConfig} = require('jest');

module.exports = defineConfig({
  extensionsToTreatAsEsm: ['.ts'],
});
precaución

Jest's ESM support is still experimental, see its docs for more details.

fakeTimers [object]​

Default: {}

The fake timers may be useful when a piece of code sets a long timeout that we don't want to wait for in a test. For additional details see Fake Timers guide and API documentation.

This option provides the default configuration of fake timers for all tests. Calling jest.useFakeTimers() in a test file will use these options or will override them if a configuration object is passed. For example, you can tell Jest to keep the original implementation of process.nextTick() and adjust the limit of recursive timers that will be run:

jest.config.js
const {defineConfig} = require('jest');

module.exports = defineConfig({
  fakeTimers: {
    doNotFake: ['nextTick'],
    timerLimit: 1000,
  },
});
fakeTime.test.js
// install fake timers for this file using the options from Jest configuration
jest.useFakeTimers();

test('increase the limit of recursive timers for this and following tests', () => {
  jest.useFakeTimers({timerLimit: 5000});
  // ...
});
consejo

Instead of including jest.useFakeTimers() in each test file, you can enable fake timers globally for all tests in your Jest configuration:

jest.config.js
const {defineConfig} = require('jest');

module.exports = defineConfig({
  fakeTimers: {
    enableGlobally: true,
  },
});

Configuration options:

type FakeableAPI =
  | 'Date'
  | 'hrtime'
  | 'nextTick'
  | 'performance'
  | 'queueMicrotask'
  | 'requestAnimationFrame'
  | 'cancelAnimationFrame'
  | 'requestIdleCallback'
  | 'cancelIdleCallback'
  | 'setImmediate'
  | 'clearImmediate'
  | 'setInterval'
  | 'clearInterval'
  | 'setTimeout'
  | 'clearTimeout';

type ModernFakeTimersConfig = {
  /**
   * If set to `true` all timers will be advanced automatically by 20 milliseconds
   * every 20 milliseconds. A custom time delta may be provided by passing a number.
   * The default is `false`.
   */
  advanceTimers?: boolean | number;
  /**
   * List of names of APIs that should not be faked. The default is `[]`, meaning
   * all APIs are faked.
   */
  doNotFake?: Array<FakeableAPI>;
  /** Whether fake timers should be enabled for all test files. The default is `false`. */
  enableGlobally?: boolean;
  /**
   * Use the old fake timers implementation instead of one backed by `@sinonjs/fake-timers`.
   * The default is `false`.
   */
  legacyFakeTimers?: boolean;
  /** Sets current system time to be used by fake timers, in milliseconds. The default is `Date.now()`. */
  now?: number;
  /** Maximum number of recursive timers that will be run. The default is `100_000` timers. */
  timerLimit?: number;
};
Legacy Fake Timers

For some reason you might have to use legacy implementation of fake timers. Here is how to enable it globally (additional options are not supported):

jest.config.js
const {defineConfig} = require('jest');

module.exports = defineConfig({
  fakeTimers: {
    enableGlobally: true,
    legacyFakeTimers: true,
  },
});

forceCoverageMatch [array<string>]​

Default: ['']

Test files are normally ignored from collecting code coverage. With this option, you can overwrite this behavior and include otherwise ignored files in code coverage.

For example, if you have tests in source files named with .t.js extension as following:

sum.t.js
export function sum(a, b) {
  return a + b;
}

if (process.env.NODE_ENV === 'test') {
  test('sum', () => {
    expect(sum(1, 2)).toBe(3);
  });
}

You can collect coverage from those files with setting forceCoverageMatch.

jest.config.js
const {defineConfig} = require('jest');

module.exports = defineConfig({
  forceCoverageMatch: ['**/*.t.js'],
});

globals [object]​

Default: {}

A set of global variables that need to be available in all test environments.

For example, the following would create a global __DEV__ variable set to true in all test environments:

jest.config.js
const {defineConfig} = require('jest');

module.exports = defineConfig({
  globals: {
    __DEV__: true,
  },
});
nota

If you specify a global reference value (like an object or array) here, and some code mutates that value in the midst of running a test, that mutation will not be persisted across test runs for other test files. In addition, the globals object must be json-serializable, so it can't be used to specify global functions. For that, you should use setupFiles.

globalSetup [string]​

Default: undefined

This option allows the use of a custom global setup module, which must export a function (it can be sync or async). The function will be triggered once before all test suites and it will receive two arguments: Jest's globalConfig and projectConfig.

información

A global setup module configured in a project (using multi-project runner) will be triggered only when you run at least one test from this project.

Any global variables that are defined through globalSetup can only be read in globalTeardown. You cannot retrieve globals defined here in your test suites.

While code transformation is applied to the linked setup-file, Jest will not transform any code in node_modules. This is due to the need to load the actual transformers (e.g. babel or typescript) to perform transformation.

setup.js
module.exports = async function (globalConfig, projectConfig) {
  console.log(globalConfig.testPathPatterns);
  console.log(projectConfig.cache);

  // Set reference to mongod in order to close the server during teardown.
  globalThis.__MONGOD__ = mongod;
};
teardown.js
module.exports = async function (globalConfig, projectConfig) {
  console.log(globalConfig.testPathPatterns);
  console.log(projectConfig.cache);

  await globalThis.__MONGOD__.stop();
};

globalTeardown [string]​

Default: undefined

This option allows the use of a custom global teardown module which must export a function (it can be sync or async). The function will be triggered once after all test suites and it will receive two arguments: Jest's globalConfig and projectConfig.

información

A global teardown module configured in a project (using multi-project runner) will be triggered only when you run at least one test from this project.

The same caveat concerning transformation of node_modules as for globalSetup applies to globalTeardown.

haste [object]​

Default: undefined

This will be used to configure the behavior of jest-haste-map, Jest's internal file crawler/cache system. The following options are supported:

type HasteConfig = {
  /** Whether to hash files using SHA-1. */
  computeSha1?: boolean;
  /** The platform to use as the default, e.g. 'ios'. */
  defaultPlatform?: string | null;
  /**
   * Force use of Node's `fs` APIs (via `fdir`) rather than shelling out to
   * the system `find` binary. Defaults to `false` on Linux/macOS.
   *
   * **Consider setting this to `true`**: `find(1)` receives no ignore
   * predicate, so it traverses ignored directories (e.g. `node_modules`,
   * `.git`) in full and discards the results afterward. The Node `fs` crawler
   * prunes those subtrees at `readdir` time. For most projects where
   * `node_modules` dwarfs source files, this makes the Node crawler faster
   * in practice despite `find(1)` being native code. A future Jest version
   * may flip this default.
   */
  forceNodeFilesystemAPI?: boolean;
  /**
   * Whether to follow symlinks when crawling for files.
   *   This option cannot be used in projects which use watchman.
   *   Projects with `watchman` set to true will error if this option is set to true.
   */
  enableSymlinks?: boolean;
  /** Path to a custom implementation of Haste. */
  hasteImplModulePath?: string;
  /** All platforms to target, e.g ['ios', 'android']. */
  platforms?: Array<string>;
  /** Whether to throw an error on module collision. */
  throwOnModuleCollision?: boolean;
  /** Custom HasteMap module */
  hasteMapModulePath?: string;
  /** Whether to retain all files, allowing e.g. search for tests in `node_modules`. */
  retainAllFiles?: boolean;
};

injectGlobals [boolean]​

Default: true

Insert Jest's globals (expect, test, describe, beforeEach etc.) into the global environment. If you set this to false, you should import from @jest/globals, e.g.

import {expect, jest, test} from '@jest/globals';

jest.useFakeTimers();

test('some test', () => {
  expect(Date.now()).toBe(0);
});
nota

This option is only supported using the default jest-circus test runner.

maxConcurrency [number]​

Default: 5

A number limiting the number of tests that are allowed to run at the same time when using test.concurrent. Any test above this limit will be queued and executed once a slot is released.

maxWorkers [number | string]​

Specifies the maximum number of workers the worker-pool will spawn for running tests. In single run mode, this defaults to the number of the cores available on your machine minus one for the main thread. In watch mode, this defaults to half of the available cores on your machine to ensure Jest is unobtrusive and does not grind your machine to a halt. It may be useful to adjust this in resource limited environments like CIs but the defaults should be adequate for most use-cases.

For environments with variable CPUs available, you can use percentage based configuration:

jest.config.js
const {defineConfig} = require('jest');

module.exports = defineConfig({
  maxWorkers: '50%',
});

moduleDirectories [array<string>]​

Default: ["node_modules"]

An array of directory names to be searched recursively up from the requiring module's location. Setting this option will override the default, if you wish to still search node_modules for packages include it along with any other options:

jest.config.js
const {defineConfig} = require('jest');

module.exports = defineConfig({
  moduleDirectories: ['node_modules', 'bower_components'],
});
precaución

It is discouraged to use '.' as one of the moduleDirectories, because this prevents scoped packages such as @emotion/react from accessing packages with the same subdirectory name (react). See this issue for more details. In most cases, it is preferable to use the moduleNameMapper configuration instead.

moduleFileExtensions [array<string>]​

Default: ["js", "mjs", "cjs", "jsx", "ts", "mts", "cts", "tsx", "json", "node"]

An array of file extensions your modules use. If you require modules without specifying a file extension, these are the extensions Jest will look for, in left-to-right order.

We recommend placing the extensions most commonly used in your project on the left, so if you are using TypeScript, you may want to consider moving "ts" and/or "tsx" to the beginning of the array.

moduleNameMapper [object<string, string | array<string>>]​

Default: null

A map from regular expressions to module names or to arrays of module names that allow to stub out resources, like images or styles with a single module.

Modules that are mapped to an alias are unmocked by default, regardless of whether automocking is enabled or not.

Use <rootDir> string token to refer to rootDir value if you want to use file paths.

Additionally, you can substitute captured regex groups using numbered backreferences.

jest.config.js
const {defineConfig} = require('jest');

module.exports = defineConfig({
  moduleNameMapper: {
    '^image![a-zA-Z0-9$_-]+$': 'GlobalImageStub',
    '^[./a-zA-Z0-9$_-]+\\.png$': '<rootDir>/RelativeImageStub.js',
    'module_name_(.*)': '<rootDir>/substituted_module_$1.js',
    'assets/(.*)': [
      '<rootDir>/images/$1',
      '<rootDir>/photos/$1',
      '<rootDir>/recipes/$1',
    ],
  },
});

The order in which the mappings are defined matters. Patterns are checked one by one until one fits. The most specific rule should be listed first. This is true for arrays of module names as well.

información

If you provide module names without boundaries ^$ it may cause hard to spot errors. E.g. relay will replace all modules which contain relay as a substring in its name: relay, react-relay and graphql-relay will all be pointed to your stub.

modulePathIgnorePatterns [array<string>]​

Default: []

An array of regexp pattern strings that are matched against all module paths before those paths are to be considered 'visible' to the module loader. If a given module's path matches any of the patterns, it will not be require()-able in the test environment.

These pattern strings match against the full path. Use the <rootDir> string token to include the path to your project's root directory to prevent it from accidentally ignoring all of your files in different environments that may have different root directories.

jest.config.js
const {defineConfig} = require('jest');

module.exports = defineConfig({
  modulePathIgnorePatterns: ['<rootDir>/build/'],
});

modulePaths [array<string>]​

Default: []

An alternative API to setting the NODE_PATH env variable, modulePaths is an array of absolute paths to additional locations to search when resolving modules. Use the <rootDir> string token to include the path to your project's root directory.

jest.config.js
const {defineConfig} = require('jest');

module.exports = defineConfig({
  modulePaths: ['<rootDir>/app/'],
});

notify [boolean]​

Default: false

Activates native OS notifications for test results. To display the notifications Jest needs node-notifier package, which must be installed additionally:

npm install --save-dev node-notifier
consejo

On macOS, remember to allow notifications from terminal-notifier under System Preferences > Notifications & Focus.

On Windows, node-notifier creates a new start menu entry on the first use and not display the notification. Notifications will be properly displayed on subsequent runs.

notifyMode [string]​

Default: failure-change

Specifies notification mode. Requires notify: true.

Modes​

  • always: always send a notification.
  • failure: send a notification when tests fail.
  • success: send a notification when tests pass.
  • change: send a notification when the status changed.
  • success-change: send a notification when tests pass or once when it fails.
  • failure-change: send a notification when tests fail or once when it passes.

openHandlesTimeout [number]​

Default: 1000

Print a warning indicating that there are probable open handles if Jest does not exit cleanly this number of milliseconds after it completes. Use 0 to disable the warning.

preset [string]​

Default: undefined

A preset that is used as a base for Jest's configuration. A preset should point to an npm module that has a jest-preset.json, jest-preset.js, jest-preset.cjs or jest-preset.mjs file at the root.

For example, this preset foo-bar/jest-preset.js will be used as follows:

jest.config.js
const {defineConfig} = require('jest');

module.exports = defineConfig({
  preset: 'foo-bar',
});

Presets may also be relative to filesystem paths:

jest.config.js
const {defineConfig} = require('jest');

module.exports = defineConfig({
  preset: './node_modules/foo-bar/jest-preset.js',
});
información

If you also have specified rootDir, the resolution of this file will be relative to that root directory.

prettierPath [string]​

Default: 'prettier'

Sets the path to the prettier node module used to update inline snapshots.

projects [array<string | ProjectConfig>]​

Default: undefined

When the projects configuration is provided with an array of paths or glob patterns, Jest will run tests in all of the specified projects at the same time. This is great for monorepos or when working on multiple projects at the same time.

jest.config.js
const {defineConfig} = require('jest');

module.exports = defineConfig({
  projects: ['<rootDir>', '<rootDir>/examples/*'],
});

This example configuration will run Jest in the root directory as well as in every folder in the examples directory. You can have an unlimited amount of projects running in the same Jest instance.

The projects feature can also be used to run multiple configurations or multiple runners. For this purpose, you can pass an array of configuration objects. For example, to run both tests and ESLint (via jest-runner-eslint) in the same invocation of Jest:

jest.config.js
const {defineConfig} = require('jest');

module.exports = defineConfig({
  projects: [
    {
      displayName: 'test',
    },
    {
      displayName: 'lint',
      runner: 'jest-runner-eslint',
      testMatch: ['<rootDir>/**/*.js'],
    },
  ],
});
consejo

When using multi-project runner, it's recommended to add a displayName for each project. This will show the displayName of a project next to its tests.

nota

With the projects option enabled, Jest will copy the root-level configuration options to each individual child configuration during the test run, resolving its values in the child's context. This means that string tokens like <rootDir> will point to the child's root directory even if they are defined in the root-level configuration.

nota

Some options only take effect at the root (global) config level and are ignored when set inside a project config. These include: bail, changedSince, ci, coverageReporters, coverageThreshold, forceExit, maxConcurrency, passWithNoTests, reporters, testResultsProcessor, testSequencer, watch, watchAll, and watchPlugins. If you need to use any of these options, define them in the root config instead of a project config.

The jest package exports the ProjectConfig and GlobalConfig TypeScript types if you need to distinguish between the two:

import type {GlobalConfig, ProjectConfig} from 'jest';

randomize [boolean]​

Default: false

The equivalent of the --randomize flag to randomize the order of the tests in a file.

reporters [array<moduleName | [moduleName, options]>]​

Default: undefined

Use this configuration option to add reporters to Jest. It must be a list of reporter names, additional options can be passed to a reporter using the tuple form:

jest.config.js
const {defineConfig} = require('jest');

module.exports = defineConfig({
  reporters: [
    'default',
    ['<rootDir>/custom-reporter.js', {banana: 'yes', pineapple: 'no'}],
  ],
});

Default Reporter​

If custom reporters are specified, the default Jest reporter will be overridden. If you wish to keep it, 'default' must be passed as a reporters name:

jest.config.js
const {defineConfig} = require('jest');

module.exports = defineConfig({
  reporters: [
    'default',
    ['jest-junit', {outputDirectory: 'reports', outputName: 'report.xml'}],
  ],
});

GitHub Actions Reporter​

If included in the list, the built-in GitHub Actions Reporter will annotate changed files with test failure messages and (if used with 'silent: false') print logs with github group features for easy navigation. Note that 'default' should not be used in this case as 'github-actions' will handle that already, so remember to also include 'summary'. If you wish to use it only for annotations simply leave only the reporter without options as the default value of 'silent' is 'true':

jest.config.js
const {defineConfig} = require('jest');

module.exports = defineConfig({
  reporters: [['github-actions', {silent: false}], 'summary'],
});

Summary Reporter​

Summary reporter prints out summary of all tests. It is a part of default reporter, hence it will be enabled if 'default' is included in the list. For instance, you might want to use it as stand-alone reporter instead of the default one, or together with Silent Reporter:

jest.config.js
const {defineConfig} = require('jest');

module.exports = defineConfig({
  reporters: ['jest-silent-reporter', 'summary'],
});

The summary reporter accepts options. Since it is included in the default reporter you may also pass the options there.

jest.config.js
const {defineConfig} = require('jest');

module.exports = defineConfig({
  reporters: [['default', {summaryThreshold: 10}]],
});

The summaryThreshold option behaves in the following way, if the total number of test suites surpasses this threshold, a detailed summary of all failed tests will be printed after executing all the tests. It defaults to 20.

Custom Reporters​

consejo

Hungry for reporters? Take a look at long list of awesome reporters from Awesome Jest.

Custom reporter module must export a class that takes globalConfig, reporterOptions and reporterContext as constructor arguments:

custom-reporter.js
class CustomReporter {
  constructor(globalConfig, reporterOptions, reporterContext) {
    this._globalConfig = globalConfig;
    this._options = reporterOptions;
    this._context = reporterContext;
  }

  onRunComplete(testContexts, results) {
    console.log('Custom reporter output:');
    console.log('global config:', this._globalConfig);
    console.log('options for this reporter from Jest config:', this._options);
    console.log('reporter context passed from test scheduler:', this._context);
  }

  // Optionally, reporters can force Jest to exit with non zero code by returning
  // an `Error` from `getLastError()` method.
  getLastError() {
    if (this._shouldFail) {
      return new Error('Custom error reported!');
    }
  }
}

module.exports = CustomReporter;
nota

For the full list of hooks and argument types see the Reporter interface in packages/jest-reporters/src/types.ts.

resetMocks [boolean]​

Default: false

Automatically reset mock state before every test. Equivalent to calling jest.resetAllMocks() before each test. This will lead to any mocks having their fake implementations removed but does not restore their initial implementation.

resetModules [boolean]​

Default: false

By default, each test file gets its own independent module registry. Enabling resetModules goes a step further and resets the module registry before running each individual test. This is useful to isolate modules for every test so that the local module state doesn't conflict between tests. This can be done programmatically using jest.resetModules().

resolver [string]​

Default: undefined

This option allows the use of a custom resolver. This resolver must be a module that exports either:

  1. a function expecting a string as the first argument for the path to resolve and an options object as the second argument. The function should either return a path to the module that should be resolved or throw an error if the module can't be found. or
  2. an object containing async and/or sync properties. The sync property should be a function with the shape explained above, and the async property should also be a function that accepts the same arguments, but returns a promise which resolves with the path to the module or rejects with an error.

The options object provided to resolvers has the shape:

type ResolverOptions = {
  /** Directory to begin resolving from. */
  basedir: string;
  /** List of export conditions. */
  conditions?: Array<string>;
  /** Instance of default resolver. */
  defaultResolver: (path: string, options: ResolverOptions) => string;
  /** List of file extensions to search in order. */
  extensions?: Array<string>;
  /** List of directory names to be looked up for modules recursively. */
  moduleDirectory?: Array<string>;
  /** List of `require.paths` to use if nothing is found in `node_modules`. */
  paths?: Array<string>;
  /** Current root directory. */
  rootDir?: string;
};
consejo

The defaultResolver passed as an option is the Jest default resolver which might be useful when you write your custom one. It takes the same arguments as your custom synchronous one, e.g. (path, options) and returns a string or throws.

For example, if you want to respect Browserify's "browser" field, you can use the following resolver:

resolver.js
const browserResolve = require('browser-resolve');

module.exports = browserResolve.sync;

And add it to Jest configuration:

jest.config.js
const {defineConfig} = require('jest');

module.exports = defineConfig({
  resolver: '<rootDir>/resolver.js',
});

Jest's jest-resolve relies on unrs-resolver. We can pass additional options, for example modifying mainFields for resolution. For example, for React Native projects, you might want to use this config:

module.exports = (path, options) => {
  // Call the defaultResolver, so we leverage its cache, error handling, etc.
  return options.defaultResolver(path, {
    ...options,
    // `unrs-resolver` option: https://github.com/unrs/unrs-resolver#main-field
    mainFields: ['react-native', 'main'],
  });
};

You can also use defaultResolver to implement a "pre-processor" that allows us to change how the default resolver will resolve modules. For example, suppose a TypeScript project needs to reference .js files at runtime but runs Jest on the .ts files.

module.exports = (path, options) => {
  // Dynamic imports within our codebase that reference .js need to reference
  // .ts during tests.
  if (
    !options.basedir.includes('node_modules') &&
    path.endsWith('.js') &&
    (path.startsWith('../') || path.startsWith('./'))
  ) {
    path = path.replace(/\.js$/, '.ts');
  }

  // Call the defaultResolver, so we leverage its cache, error handling, etc.
  return options.defaultResolver(path, options);
};

restoreMocks [boolean]​

Default: false

Automatically restore mock state and implementation before every test. Equivalent to calling jest.restoreAllMocks() before each test. This will lead to any mocks having their fake implementations removed and restores their initial implementation.

rootDir [string]​

Default: The root of the directory containing your Jest config file or the package.json or the pwd if no package.json is found

The root directory that Jest should scan for tests and modules within. If you put your Jest config inside your package.json and want the root directory to be the root of your repo, the value for this config param will default to the directory of the package.json.

Oftentimes, you'll want to set this to 'src' or 'lib', corresponding to where in your repository the code is stored.

consejo

Using '<rootDir>' as a string token in any other path-based configuration settings will refer back to this value. For example, if you want a setupFiles entry to point at the some-setup.js file at the root of the project, set its value to: '<rootDir>/some-setup.js'.

roots [array<string>]​

Default: ["<rootDir>"]

A list of paths to directories that Jest should use to search for files in.

There are times where you only want Jest to search in a single sub-directory (such as cases where you have a src/ directory in your repo), but prevent it from accessing the rest of the repo.

información

While rootDir is mostly used as a token to be re-used in other configuration options, roots is used by the internals of Jest to locate test files and source files. This applies also when searching for manual mocks for modules from node_modules (__mocks__ will need to live in one of the roots).

By default, roots has a single entry <rootDir> but there are cases where you may want to have multiple roots within one project, for example roots: ["<rootDir>/src/", "<rootDir>/tests/"].

runtime [string]​

Default: "jest-runtime"

This option allows the use of a custom runtime to execute test files. A custom runtime can be provided by specifying a path to a runtime implementation.

The runtime module must export a class that extends Jest's default Runtime class or implements a compatible interface with the same constructor signature and methods.

aviso

Creating a custom runtime is an advanced use case. Most users should not need to customize the runtime. Consider whether your use case might be better addressed with custom transformers, test environments, or module mocks.

Example:

custom-runtime.js
const {default: Runtime} = require('jest-runtime');

class CustomRuntime extends Runtime {
  //...custom logic
}

module.exports = CustomRuntime;
custom-runtime.ts
import Runtime from 'jest-runtime';

export default class CustomRuntime extends Runtime {
  //...custom logic
}

Add the custom runtime to your Jest configuration:

jest.config.js
const {defineConfig} = require('jest');

module.exports = defineConfig({
  runtime: './custom-runtime.js',
});

runner [string | [string, object]]​

Default: "jest-runner"

This option allows you to use a custom runner instead of Jest's default test runner. Examples of runners include:

información

The runner property value can omit the jest-runner- prefix of the package name.

You can pass options to a custom runner by using a tuple form. The options will be passed as the third argument to the runner's constructor:

jest.config.js
const {defineConfig} = require('jest');

module.exports = defineConfig({
  runner: ['jest-runner-custom', {myOption: true, timeout: 5000}],
});

To write a custom test-runner, export a class that extends one of the base runners from jest-runner (CallbackTestRunner or EmittingTestRunner) and implements the runTests method. When using the tuple configuration, the options object is passed as the third constructor argument:

my-runner.js
const {CallbackTestRunner} = require('jest-runner');

class MyRunner extends CallbackTestRunner {
  constructor(globalConfig, context, options) {
    super(globalConfig, context);
    this._runnerOptions = options;
  }

  async runTests(tests, watcher, onStart, onResult, onFailure, options) {
    // implement test execution using this._runnerOptions
  }
}

module.exports = MyRunner;

If you need to restrict your test-runner to only run in serial rather than being executed in parallel your class should have the property isSerial to be set as true.

sandboxInjectedGlobals [array<string>]​

consejo

Renamed from extraGlobals in Jest 28.

Default: undefined

Test files run inside a vm, which slows calls to global context properties (e.g. Math). With this option you can specify extra properties to be defined inside the vm for faster lookups.

For example, if your tests call Math often, you can pass it by setting sandboxInjectedGlobals.

jest.config.js
const {defineConfig} = require('jest');

module.exports = defineConfig({
  sandboxInjectedGlobals: ['Math'],
});
nota

This option has no effect if you use native ESM.

setupFiles [array]​

Default: []

A list of paths to modules that run some code to configure or set up the testing environment. Each setupFile will be run once per test file. Since every test runs in its own environment, these scripts will be executed in the testing environment before executing setupFilesAfterEnv and before the test code itself.

consejo

If your setup script is a CJS module, it may export an async function. Jest will call the function and await its result. This might be useful to fetch some data asynchronously. If the file is an ESM module, simply use top-level await to achieve the same result.

setupFilesAfterEnv [array]​

Default: []

A list of paths to modules that run some code to configure or set up the testing framework before each test file in the suite is executed. Since setupFiles executes before the test framework is installed in the environment, this script file presents you the opportunity of running some code immediately after the test framework has been installed in the environment but before the test code itself.

In other words, setupFilesAfterEnv modules are meant for code which is repeating in each test file. Having the test framework installed makes Jest globals, jest object and expect accessible in the modules. For example, you can add extra matchers from jest-extended library or call setup and teardown hooks:

setup-jest.js
const matchers = require('jest-extended');
expect.extend(matchers);

afterEach(() => {
  jest.useRealTimers();
});
jest.config.js
const {defineConfig} = require('jest');

module.exports = defineConfig({
  setupFilesAfterEnv: ['<rootDir>/setup-jest.js'],
});
consejo

If your setup script is a CJS module, it may export an async function. Jest will call the function and await its result. This might be useful to fetch some data asynchronously. If the file is an ESM module, simply use top-level await to achieve the same result.

showSeed [boolean]​

Default: false

The equivalent of the --showSeed flag to print the seed in the test report summary.

slowTestThreshold [number]​

Default: 5

The number of seconds after which a test is considered as slow and reported as such in the results.

snapshotFormat [object]​

Default: {escapeString: false, printBasicPrototype: false}

Allows overriding specific snapshot formatting options documented in the pretty-format readme, with the exceptions of compareKeys and plugins. For example, this config would have the snapshot formatter not print a prefix for "Object" and "Array":

jest.config.js
const {defineConfig} = require('jest');

module.exports = defineConfig({
  snapshotFormat: {
    printBasicPrototype: false,
  },
});
some.test.js
test('does not show prototypes for object and array inline', () => {
  const object = {
    array: [{hello: 'Danger'}],
  };
  expect(object).toMatchInlineSnapshot(`
    {
      "array": [
        {
          "hello": "Danger",
        },
      ],
    }
  `);
});

snapshotResolver [string]​

Default: undefined

The path to a module that can resolve test<->snapshot path. This config option lets you customize where Jest stores snapshot files on disk.

custom-resolver.js
module.exports = {
  // resolves from test to snapshot path
  resolveSnapshotPath: (testPath, snapshotExtension) =>
    testPath.replace('__tests__', '__snapshots__') + snapshotExtension,

  // resolves from snapshot to test path
  resolveTestPath: (snapshotFilePath, snapshotExtension) =>
    snapshotFilePath
      .replace('__snapshots__', '__tests__')
      .slice(0, -snapshotExtension.length),

  // Example test path, used for preflight consistency check of the implementation above
  testPathForConsistencyCheck: 'some/__tests__/example.test.js',
};

snapshotSerializers [array<string>]​

Default: []

A list of paths to snapshot serializer modules Jest should use for snapshot testing.

Jest has default serializers for built-in JavaScript types, HTML elements (Jest 20.0.0+), ImmutableJS (Jest 20.0.0+) and for React elements. See snapshot test tutorial for more information.

custom-serializer.js
module.exports = {
  serialize(val, config, indentation, depth, refs, printer) {
    return `Pretty foo: ${printer(val.foo, config, indentation, depth, refs)}`;
  },

  test(val) {
    return val && Object.prototype.hasOwnProperty.call(val, 'foo');
  },
};

printer is a function that serializes a value using existing plugins.

Add custom-serializer to your Jest configuration:

jest.config.js
const {defineConfig} = require('jest');

module.exports = defineConfig({
  snapshotSerializers: ['path/to/custom-serializer.js'],
});

Finally tests would look as follows:

test(() => {
  const bar = {
    foo: {
      x: 1,
      y: 2,
    },
  };

  expect(bar).toMatchSnapshot();
});

Rendered snapshot:

Pretty foo: Object {
  "x": 1,
  "y": 2,
}
consejo

To make a dependency explicit instead of implicit, you can call expect.addSnapshotSerializer to add a module for an individual test file instead of adding its path to snapshotSerializers in Jest configuration.

More about serializers API can be found here.

testEnvironment [node | jsdom | string]​

Default: node

The test environment that will be used for testing. The default environment in Jest is a Node.js environment. If you are building a web app, you can use a browser-like environment through jsdom instead.

By adding a @jest-environment docblock at the top of the file, you can specify another environment to be used for all tests in that file:

  • With built-in environments:
my-test.spec.js
/**
 * @jest-environment jsdom
 */

test('use jsdom in this test file', () => {
  const element = document.createElement('div');
  expect(element).not.toBeNull();
});
  • With custom environment:
my-test.spec.js
/**
 * @jest-environment ./my-custom-environment.js
 */

test('use jsdom in this test file', () => {
  const element = document.createElement('div');
  expect(element).not.toBeNull();
});

You can also define custom environment. When non-builtin environment is used, Jest will try to load either the file path or the package name defined as value for testEnvironment. That file or the package should export an object with the shape of JestEnvironment:

environment.js
/**
 * @implements {import('@jest/environment').JestEnvironment}
 */
class CustomEnvironment {
  constructor(config, context) {
    const {projectConfig} = config;
    // Implement the constructor
  }

  // Example of a method
  getVmContext() {
    return null;
  }
  // Implement the required methods here
}

module.exports = CustomEnvironment;

Jest also exposes builtinEnvironments through jest-environment-node and jest-environment-jsdom packages, in case you just want to extend it. You can read more about extending environments in our guide.

testEnvironmentOptions [Object]​

Default: {}

Test environment options that will be passed to the testEnvironment. The relevant options depend on the environment being used.

Node Environment Options​

When using the node environment, you can configure various options that are passed to runInContext. These options include:

  • globalsCleanup ('on' | 'soft' | 'off'): Controls cleanup of global variables between tests. Default: 'soft'.
  • All the options listed in the vm.runInContext documentation

JSDOM Environment Options​

When using the jsdom environment, you can configure various options that are passed to jsdom. These options include:

  • url - The URL of the page (affects window.location and relative URLs). Default: "http://localhost"
  • userAgent - The user agent string. Default: a generic user agent
  • All the options listed in the jsdom

For example, you can override options passed to jsdom:

jest.config.js
const {defineConfig} = require('jest');

module.exports = defineConfig({
  testEnvironment: 'jsdom',
  testEnvironmentOptions: {
    html: '<html lang="en-US"></html>',
    url: 'https://jestjs.io/',
    userAgent: 'Agent/007',
  },
});

Custom Export Conditions​

The testEnvironmentOptions allow specifying customExportConditions, which control which versions of a library are loaded from exports in package.json.

The built-in environments have the following defaults:

  • jest-environment-jsdom defaults to ['browser']
  • jest-environment-node defaults to ['node', 'node-addons']

For example, you can override customExportConditions passed to jsdom:

jest.config.js
const {defineConfig} = require('jest');

module.exports = defineConfig({
  testEnvironment: 'jsdom',
  testEnvironmentOptions: {
    customExportConditions: ['react-native'],
  },
});

These options can also be passed in a docblock, similar to testEnvironment. The string with options must be parseable by JSON.parse:

/**
 * @jest-environment jsdom
 * @jest-environment-options {"url": "https://jestjs.io/"}
 */

test('use jsdom and set the URL in this test file', () => {
  expect(window.location.href).toBe('https://jestjs.io/');
});

You can combine multiple options:

/**
 * @jest-environment jsdom
 * @jest-environment-options {"url": "https://example.com/", "userAgent": "Custom Agent"}
 */

test('use custom URL and user agent', () => {
  expect(window.location.href).toBe('https://example.com/');
  expect(window.navigator.userAgent).toContain('Custom Agent');
});

testFailureExitCode [number]​

Default: 1

The exit code Jest returns on test failure.

información

This does not change the exit code in the case of Jest errors (e.g. invalid configuration).

testMatch [array<string>]​

(default: [ "**/__tests__/**/*.?([mc])[jt]s?(x)", "**/?(*.)+(spec|test).?([mc])[jt]s?(x)" ])

The glob patterns Jest uses to detect test files. By default it looks for .js, .jsx, .ts and .tsx files inside of __tests__ folders, as well as any files with a suffix of .test or .spec (e.g. Component.test.js or Component.spec.js). It will also find files called test.js or spec.js.

See the micromatch package for details of the patterns you can specify.

See also testRegex [string | array<string>], but note that you cannot specify both options.

consejo

Each glob pattern is applied in the order they are specified in the config. For example ["!**/__fixtures__/**", "**/__tests__/**/*.js"] will not exclude __fixtures__ because the negation is overwritten with the second pattern. In order to make the negated glob work in this example it has to come after **/__tests__/**/*.js.

testPathIgnorePatterns [array<string>]​

Default: ["/node_modules/"]

An array of regexp pattern strings that are matched against all test paths before executing the test. If the test path matches any of the patterns, it will be skipped.

These pattern strings match against the full path. Use the <rootDir> string token to include the path to your project's root directory to prevent it from accidentally ignoring all of your files in different environments that may have different root directories. Example: ["<rootDir>/build/", "<rootDir>/node_modules/"].

testRegex [string | array<string>]​

Default: (/__tests__/.*|(\\.|/)(test|spec))\\.[mc]?[jt]sx?$

The pattern or patterns Jest uses to detect test files. By default it looks for .js, .jsx, .ts and .tsx files inside of __tests__ folders, as well as any files with a suffix of .test or .spec (e.g. Component.test.js or Component.spec.js). It will also find files called test.js or spec.js. See also testMatch [array<string>], but note that you cannot specify both options.

The following is a visualization of the default regex:

├── __tests__
│   └── component.spec.js # test
│   └── anything # test
├── package.json # not test
├── foo.test.js # test
├── bar.spec.jsx # test
└── component.js # not test
información

testRegex will try to detect test files using the absolute file path, therefore, having a folder with a name that matches it will run all the files as tests.

testResultsProcessor [string]​

Default: undefined

This option allows the use of a custom results processor. This processor must be a node module that exports a function expecting an object with the following structure as the first argument and return it:

{
  "success": boolean,
  "startTime": epoch,
  "numTotalTestSuites": number,
  "numPassedTestSuites": number,
  "numFailedTestSuites": number,
  "numRuntimeErrorTestSuites": number,
  "numTotalTests": number,
  "numPassedTests": number,
  "numFailedTests": number,
  "numPendingTests": number,
  "numTodoTests": number,
  "openHandles": Array<Error>,
  "testResults": [{
    "numFailingTests": number,
    "numPassingTests": number,
    "numPendingTests": number,
    "testResults": [{
      "title": string (message in it block),
      "status": "failed" | "pending" | "passed",
      "ancestorTitles": [string (message in describe blocks)],
      "failureMessages": [string],
      "numPassingAsserts": number,
      "location": {
        "column": number,
        "line": number
      },
      "duration": number | null,
      "startAt": epoch | null
    },
    ...
    ],
    "perfStats": {
      "end": epoch,
      "loadTestEnvironmentEnd": epoch,
      "loadTestEnvironmentStart": epoch,
      "runtime": number,
      "setupAfterEnvEnd": epoch,
      "setupAfterEnvStart": epoch,
      "setupFilesEnd": epoch,
      "setupFilesStart": epoch,
      "slow": boolean,
      "start": epoch
    },
    "testFilePath": absolute path to test file,
    "coverage": {}
  },
  "testExecError:" (exists if there was a top-level failure) {
    "message": string
    "stack": string
  }
  ...
  ]
}

testResultsProcessor and reporters are very similar to each other. One difference is that a test result processor only gets called after all tests finished. Whereas a reporter has the ability to receive test results after individual tests and/or test suites are finished.

testRunner [string]​

Default: jest-circus/runner

This option allows the use of a custom test runner. The default is jest-circus. A custom test runner can be provided by specifying a path to a test runner implementation.

The test runner module must export a function with the following signature:

function testRunner(
  globalConfig: GlobalConfig,
  config: ProjectConfig,
  environment: Environment,
  runtime: Runtime,
  testPath: string,
): Promise<TestResult>;

An example of such function can be found in our default jasmine2 test runner package.

testSequencer [string]​

Default: @jest/test-sequencer

This option allows you to use a custom sequencer instead of Jest's default.

consejo

Both sort and shard may optionally return a Promise.

For example, you may sort test paths alphabetically:

custom-sequencer.js
const Sequencer = require('@jest/test-sequencer').default;

class CustomSequencer extends Sequencer {
  /**
   * Select tests for shard requested via --shard=shardIndex/shardCount
   * Sharding is applied before sorting
   */
  shard(tests, {shardIndex, shardCount}) {
    const shardSize = Math.ceil(tests.length / shardCount);
    const shardStart = shardSize * (shardIndex - 1);
    const shardEnd = shardSize * shardIndex;

    return [...tests]
      .sort((a, b) => (a.path > b.path ? 1 : -1))
      .slice(shardStart, shardEnd);
  }

  /**
   * Sort test to determine order of execution
   * Sorting is applied after sharding
   */
  sort(tests) {
    // Test structure information
    // https://github.com/jestjs/jest/blob/6b8b1404a1d9254e7d5d90a8934087a9c9899dab/packages/jest-runner/src/types.ts#L17-L21
    const copyTests = [...tests];
    return copyTests.sort((testA, testB) => (testA.path > testB.path ? 1 : -1));
  }
}

module.exports = CustomSequencer;

Add custom-sequencer to your Jest configuration:

jest.config.js
const {defineConfig} = require('jest');

module.exports = defineConfig({
  testSequencer: 'path/to/custom-sequencer.js',
});

testTimeout [number]​

Default: 5000

Default timeout of a test in milliseconds.

transform [object<string, pathToTransformer | [pathToTransformer, object]>]​

Default: {"\\.[jt]sx?$": "babel-jest"}

A map from regular expressions to paths to transformers. Optionally, a tuple with configuration options can be passed as second argument: {filePattern: ['path-to-transformer', {options}]}. For example, here is how you can configure babel-jest for non-default behavior: {'\\.js$': ['babel-jest', {rootMode: 'upward'}]}.

Jest runs the code of your project as JavaScript, hence a transformer is needed if you use some syntax not supported by Node out of the box (such as JSX, TypeScript, Vue templates). By default, Jest will use babel-jest transformer, which will load your project's Babel configuration and transform any file matching the /\.[jt]sx?$/ RegExp (in other words, any .js, .jsx, .ts or .tsx file). In addition, babel-jest will inject the Babel plugin necessary for mock hoisting talked about in ES Module mocking.

See the Code Transformation section for more details and instructions on building your own transformer.

consejo

Keep in mind that a transformer only runs once per file unless the file has changed.

Remember to include the default babel-jest transformer explicitly, if you wish to use it alongside with additional code preprocessors:

jest.config.js
const {defineConfig} = require('jest');

module.exports = defineConfig({
  transform: {
    '\\.[jt]sx?$': 'babel-jest',
    '\\.css$': 'some-css-transformer',
  },
});

transformIgnorePatterns [array<string>]​

Default: ["/node_modules/", "\\.pnp\\.[^\\\/]+$"]

An array of regexp pattern strings that are matched against all source file paths before transformation. If the file path matches any of the patterns, it will not be transformed.

Providing regexp patterns that overlap with each other may result in files not being transformed that you expected to be transformed. For example:

jest.config.js
const {defineConfig} = require('jest');

module.exports = defineConfig({
  transformIgnorePatterns: ['/node_modules/(?!(foo|bar)/)', '/bar/'],
});

The first pattern will match (and therefore not transform) files inside /node_modules except for those in /node_modules/foo/ and /node_modules/bar/. The second pattern will match (and therefore not transform) files inside any path with /bar/ in it. With the two together, files in /node_modules/bar/ will not be transformed because it does match the second pattern, even though it was excluded by the first.

Sometimes it happens (especially in React Native or TypeScript projects) that 3rd party modules are published as untranspiled code. Since all files inside node_modules are not transformed by default, Jest will not understand the code in these modules, resulting in syntax errors. To overcome this, you may use transformIgnorePatterns to allow transpiling such modules. You'll find a good example of this use case in React Native Guide.

These pattern strings match against the full path. Use the <rootDir> string token to include the path to your project's root directory to prevent it from accidentally ignoring all of your files in different environments that may have different root directories.

jest.config.js
const {defineConfig} = require('jest');

module.exports = defineConfig({
  transformIgnorePatterns: [
    '<rootDir>/bower_components/',
    '<rootDir>/node_modules/',
  ],
});
consejo

If you use pnpm and need to convert some packages under node_modules, you need to note that the packages in this folder (e.g. node_modules/package-a/) have been symlinked to the path under .pnpm (e.g. node_modules/.pnpm/[email protected]/node_modules/package-a/), so using <rootDir>/node_modules/(?!(package-a|@scope/pkg-b)/) directly will not be recognized, while is to use:

jest.config.js
const {defineConfig} = require('jest');

module.exports = defineConfig({
  transformIgnorePatterns: [
    '<rootDir>/node_modules/.pnpm/(?!(package-a|@scope\\+pkg-b)@)',
    /* if config file is under '~/packages/lib-a/' */
    `${path.join(
      __dirname,
      '../..',
    )}/node_modules/.pnpm/(?!(package-a|@scope\\+pkg-b)@)`,
    /* or using relative pattern to match the second 'node_modules/' in 'node_modules/.pnpm/@[email protected]/node_modules/@scope/pkg-b/' */
    'node_modules/(?!.pnpm|package-a|@scope/pkg-b)',
  ],
});

It should be noted that the folder name of pnpm under .pnpm is the package name plus @ and version number, so writing / will not be recognized, but using @ can.

unmockedModulePathPatterns [array<string>]​

Default: []

An array of regexp pattern strings that are matched against all modules before the module loader will automatically return a mock for them. If a module's path matches any of the patterns in this list, it will not be automatically mocked by the module loader.

This is useful for some commonly used 'utility' modules that are almost always used as implementation details almost all the time (like underscore, lodash, etc). It's generally a best practice to keep this list as small as possible and always use explicit jest.mock()/jest.unmock() calls in individual tests. Explicit per-test setup is far easier for other readers of the test to reason about the environment the test will run in.

It is possible to override this setting in individual tests by explicitly calling jest.mock() at the top of the test file.

verbose [boolean]​

Default: false or true if there is only one test file to run

Indicates whether each individual test should be reported during the run. All errors will also still be shown on the bottom after execution.

waitForUnhandledRejections [boolean]​

Gives one event loop turn to handle rejectionHandled, uncaughtException or unhandledRejection.

Without this flag Jest may report false-positive errors (e.g. actually handled rejection reported) or not report actually unhandled rejection (or report it for different test case).

This option may add a noticeable overhead for fast test suites.

watchPathIgnorePatterns [array<string>]​

Default: []

An array of RegExp patterns that are matched against all source file paths before re-running tests in watch mode. If the file path matches any of the patterns, when it is updated, it will not trigger a re-run of tests.

These patterns match against the full path. Use the <rootDir> string token to include the path to your project's root directory to prevent it from accidentally ignoring all of your files in different environments that may have different root directories. Example: ["<rootDir>/node_modules/"].

Even if nothing is specified here, the watcher will ignore changes to the version control folders (.git, .hg, .sl). Other hidden files and directories, i.e. those that begin with a dot (.), are watched by default. Remember to escape the dot when you add them to watchPathIgnorePatterns as it is a special RegExp character.

jest.config.js
const {defineConfig} = require('jest');

module.exports = defineConfig({
  watchPathIgnorePatterns: ['<rootDir>/\\.tmp/', '<rootDir>/bar/'],
});

watchPlugins [array<string | [string, Object]>]​

Default: []

This option allows you to use custom watch plugins. Read more about watch plugins here.

Examples of watch plugins include:

información

The values in the watchPlugins property value can omit the jest-watch- prefix of the package name.

watchman [boolean]​

Default: true

Whether to use watchman for file crawling.

workerGracefulExitTimeout [number]​

Default: 500

Timeout in milliseconds for a worker process to exit gracefully after all tests have completed. If a worker does not exit within this timeout, it is force-killed.

Increase this value if your test environment requires more time to tear down (for example, when using --detectOpenHandles or when workers hold onto long-lived resources).

jest.config.js
const {defineConfig} = require('jest');

module.exports = defineConfig({
  workerGracefulExitTimeout: 2000,
});

workerIdleMemoryLimit [number|string]​

Default: undefined

Specifies the memory limit for workers before they are recycled and is primarily a work-around for this issue;

After the worker has executed a test the memory usage of it is checked. If it exceeds the value specified the worker is killed and restarted. The limit can be specified in a number of different ways and whatever the result is Math.floor is used to turn it into an integer value:

  • <= 1 - The value is assumed to be a percentage of system memory. So 0.5 sets the memory limit of the worker to half of the total system memory
  • \> 1 - Assumed to be a fixed byte value. Because of the previous rule if you wanted a value of 1 byte (I don't know why) you could use 1.1.
  • With units
    • 50% - As above, a percentage of total system memory
    • 100KB, 65MB, etc - With units to denote a fixed memory limit.
      • K / KB - Kilobytes (x1000)
      • KiB - Kibibytes (x1024)
      • M / MB - Megabytes
      • MiB - Mebibytes
      • G / GB - Gigabytes
      • GiB - Gibibytes
precaución

Percentage based memory limit does not work on Linux CircleCI workers due to incorrect system memory being reported.

jest.config.js
const {defineConfig} = require('jest');

module.exports = defineConfig({
  workerIdleMemoryLimit: 0.2,
});

// [string]​

This option allows comments in package.json. Include the comment text as the value of this key:

package.json
{
  "name": "my-project",
  "jest": {
    "//": "Comment goes here",
    "verbose": true
  }
}

workerThreads​

Default: false

Whether to use worker threads for parallelization. Child processes are used by default.

Using worker threads may help to improve performance.

precaución

This is experimental feature. Keep in mind that the worker threads use structured clone instead of JSON.stringify() to serialize messages. This means that built-in JavaScript objects as BigInt, Map or Set will get serialized properly. However extra properties set on Error, Map or Set will not be passed on through the serialization step. For more details see the article on structured clone.