Configuring Jest

Jest's configuration can be defined in the package.json file of your project, or through a jest.config.js, or jest.config.ts file or through the --config <path/to/file.js|ts|cjs|mjs|json> option. If you'd like to use your package.json to store Jest's config, the "jest" key should be used on the top level so Jest will know how to find your settings:

{
  "name": "my-project",
  "jest": {
    "verbose": true
  }
}

Or through JavaScript:

// Sync object
/** @type {import('@jest/types').Config.InitialOptions} */
const config = {
  verbose: true,
};

module.exports = config;

// Or async function
module.exports = async () => {
  return {
    verbose: true,
  };
};

Or through TypeScript (if ts-node is installed):

import type {Config} from '@jest/types';

// Sync object
const config: Config.InitialOptions = {
  verbose: true,
};
export default config;

// Or async function
export default async (): Promise<Config.InitialOptions> => {
  return {
    verbose: true,
  };
};

Please keep in mind that the resulting configuration must be JSON-serializable.

When using the --config option, the JSON file must not contain a "jest" key:

{
  "bail": 1,
  "verbose": true
}

Options

These options let you control Jest's behavior in your package.json file. The Jest philosophy is to work great by default, but sometimes you just need more configuration power.

Defaults

You can retrieve Jest's default options to expand them if needed:

const {defaults} = require('jest-config');
module.exports = {
  // ...
  moduleFileExtensions: [...defaults.moduleFileExtensions, 'ts', 'tsx'],
  // ...
};

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:

export default {
  authorize: () => {
    return 'token';
  },
  isAuthorized: secret => secret === 'wizard',
};

//__tests__/automocking.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();
});

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.

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.

Example:

{
  "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/**.

=============================== 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.

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.

Note that using v8 is considered experimental. This uses V8's builtin code coverage rather than one based on Babel. It is not as well tested, and it has also improved in the last few releases of Node. Using the latest versions of node (v14 at the time of this writing) will yield better results.

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.

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

{
  "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. Thresholds specified as a positive number are taken to be the minimum percentage required. Thresholds specified as a negative number represent the maximum number of uncovered entities 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": {
    "coverageThreshold": {
      "global": {
        "branches": 80,
        "functions": 80,
        "lines": 80,
        "statements": -10
      }
    }
  }
}

If globs or paths are specified alongside global, coverage data for matching paths will be subtracted from overall coverage and thresholds will be applied independently. Thresholds for globs are applied to all files matching the glob. If the file specified by path is not found, an error is returned.

For example, with the following configuration:

{
  ...
  "jest": {
    "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 or 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.
• Every remaining file combined has 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. Here are sample valid values.

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

or

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

As a secondary option, 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.

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": {
    "extensionsToTreatAsEsm": [".ts"]
  }
}

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:

{
  "fakeTimers": {
    "doNotFake": ["nextTick"],
    "timerLimit": 1000
  }
}

// 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});
  // ...
});

{
  "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. The default is `Date.now()`. */
  now?: number;
  /** Maximum number of recursive timers that will be run. The default is `100_000` timers. */
  timerLimit?: number;
};

{
  "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:

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": {
    "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": {
    "globals": {
      "__DEV__": true
    }
  }
}

Note that, 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.

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

  // Set reference to mongod in order to close the server during teardown.
  globalThis.__MONGOD__ = mongod;
};

module.exports = async function (globalConfig, projectConfig) {
  console.log(globalConfig.testPathPattern);
  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.

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 rather than shelling out to `find` */
  forceNodeFilesystemAPI?: boolean;
  /**
   * Whether to follow symlinks when crawling for files.
   *   This options 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 on 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);
});

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: "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: ["node_modules", "bower_components"]

moduleFileExtensions [array<string>]

Default: ["js", "mjs", "cjs", "jsx", "ts", "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.

Example:

{
  "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.

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. Example: ["<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. Example: ["<rootDir>/app/"].

notify [boolean]

Default: false

Activates notifications for test results.

Beware: Jest uses node-notifier to display desktop notifications. On Windows, it 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.

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 configured as follows:

{
  "preset": "foo-bar"
}

Presets may also be relative to filesystem paths.

{
  "preset": "./node_modules/foo-bar/jest-preset.js"
}

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.

{
  "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:

{
  "projects": [
    {
      "displayName": "test"
    },
    {
      "displayName": "lint",
      "runner": "jest-runner-eslint",
      "testMatch": ["<rootDir>/**/*.js"]
    }
  ]
}

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:

{
  "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:

{
  "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:

{
  "reporters": ["default", "github-actions"]
}

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:

{
  "reporters": ["jest-silent-reporter", "summary"]
}

Custom Reporters

Custom reporter module must export a class that takes globalConfig, reporterOptions and reporterContext as constructor arguments and implements at least onRunComplete() method (for the full list of methods and argument types see Reporter interface in packages/jest-reporters/src/types.ts):

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;

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>;
  /** Allows transforming parsed `package.json` contents. */
  packageFilter?: (pkg: PackageJSON, file: string, dir: string) => PackageJSON;
  /** Allows transforms a path within a package. */
  pathFilter?: (pkg: PackageJSON, path: string, relativePath: string) => string;
  /** Current root directory. */
  rootDir?: string;
};

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

{
  "resolver": "<rootDir>/resolver.js"
}

const browserResolve = require('browser-resolve');

module.exports = browserResolve.sync;

By combining defaultResolver and packageFilter we can implement a package.json "pre-processor" that allows us to change how the default resolver will resolve modules. For example, imagine we want to use the field "module" if it is present, otherwise fallback to "main":

module.exports = (path, options) => {
  // Call the defaultResolver, so we leverage its cache, error handling, etc.
  return options.defaultResolver(request, {
    ...options,
    // Use packageFilter to process parsed `package.json` before the resolution (see https://www.npmjs.com/package/resolve#resolveid-opts-cb)
    packageFilter: pkg => {
      return {
        ...pkg,
        // Alter the value of `main` before resolving the package
        main: pkg.module || pkg.main,
      };
    },
  });
};

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.

Note that using '<rootDir>' as a string token in any other path-based config settings will refer back to this value. So, for example, if you want your setupFiles config entry to point at the env-setup.js file at the root of your project, you could set its value to ["<rootDir>/env-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.

runner [string]

Default: "jest-runner"

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

• jest-runner-eslint
• jest-runner-mocha
• jest-runner-tsc
• jest-runner-prettier

To write a test-runner, export a class with which accepts globalConfig in the constructor, and has a runTests method with the signature:

async function runTests(
  tests: Array<Test>,
  watcher: TestWatcher,
  onStart: OnTestStart,
  onResult: OnTestSuccess,
  onFailure: OnTestFailure,
  options: TestRunnerOptions,
): Promise<void>;

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>]

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": {
    "sandboxInjectedGlobals": ["Math"]
  }
}

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.

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.

If you want a path to be relative to the root directory of your project, please include <rootDir> inside a path's string, like "<rootDir>/a-configs-folder".

For example, Jest ships with several plug-ins to jasmine that work by monkey-patching the jasmine API. If you wanted to add even more jasmine plugins to the mix (or if you wanted some custom, project-wide matchers for example), you could do so in these modules.

Example setupFilesAfterEnv array in a jest.config.js:

module.exports = {
  setupFilesAfterEnv: ['./jest.setup.js'],
};

Example jest.setup.js file

jest.setTimeout(10000); // in milliseconds

// you can even use the setup/teardown methods
beforeAll(() => {
  // your code
});
beforeEach(() => {
  // your code
});
afterEach(() => {
  // your code
});
afterAll(() => {
  // your code
});

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: undefined

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": {
    "snapshotFormat": {
      "printBasicPrototype": false
    }
  }
}

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

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.

Example snapshot resolver module:

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.

Example serializer module:

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

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

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

To use my-serializer-module as a serializer, configuration would be as follows:

{
  ...
  "jest": {
    "snapshotSerializers": ["my-serializer-module"]
  }
}

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,
}

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 [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:

/**
 * @jest-environment jsdom
 */

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

You can create your own module that will be used for setting up the test environment. The module must export a class with setup, teardown and getVmContext methods. You can also pass variables from this module to your test suites by assigning them to this.global object – this will make them available in your test suites as global variables. The constructor is passed global config and project config as its first argument, and testEnvironmentContext as its second.

The class may optionally expose an asynchronous handleTestEvent method to bind to events fired by jest-circus. Normally, jest-circus test runner would pause until a promise returned from handleTestEvent gets fulfilled, except for the next events: start_describe_definition, finish_describe_definition, add_hook, add_test or error (for the up-to-date list you can look at SyncEvent type in the types definitions). That is caused by backward compatibility reasons and process.on('unhandledRejection', callback) signature, but that usually should not be a problem for most of the use cases.

Any docblock pragmas in test files will be passed to the environment constructor and can be used for per-test configuration. If the pragma does not have a value, it will be present in the object with its value set to an empty string. If the pragma is not present, it will not be present in the object.

To use this class as your custom environment, refer to it by its full path within the project. For example, if your class is stored in my-custom-environment.js in some subfolder of your project, then the annotation might look like this:

/**
 * @jest-environment ./src/test/my-custom-environment
 */

Example:

// my-custom-environment
const NodeEnvironment = require('jest-environment-node').default;

class CustomEnvironment extends NodeEnvironment {
  constructor(config, context) {
    super(config, context);
    console.log(config.globalConfig);
    console.log(config.projectConfig);
    this.testPath = context.testPath;
    this.docblockPragmas = context.docblockPragmas;
  }

  async setup() {
    await super.setup();
    await someSetupTasks(this.testPath);
    this.global.someGlobalObject = createGlobalObject();

    // Will trigger if docblock contains @my-custom-pragma my-pragma-value
    if (this.docblockPragmas['my-custom-pragma'] === 'my-pragma-value') {
      // ...
    }
  }

  async teardown() {
    this.global.someGlobalObject = destroyGlobalObject();
    await someTeardownTasks();
    await super.teardown();
  }

  getVmContext() {
    return super.getVmContext();
  }

  async handleTestEvent(event, state) {
    if (event.name === 'test_start') {
      // ...
    }
  }
}

module.exports = CustomEnvironment;

// my-test-suite
/**
 * @jest-environment ./my-custom-environment
 */
let someGlobalObject;

beforeAll(() => {
  someGlobalObject = globalThis.someGlobalObject;
});

testEnvironmentOptions [Object]

Default: {}

Test environment options that will be passed to the testEnvironment. The relevant options depend on the environment. For example, you can override options given to jsdom such as {html: "<html lang="zh-cmn-Hant"></html>", url: 'https://jestjs.io/', userAgent: "Agent/007"}.

These options can also be passed in a docblock, similar to testEnvironment. Note that it must be parseable by JSON.parse. Example:

/**
 * @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/');
});

testFailureExitCode [number]

Default: 1

The exit code Jest returns on test failure.

testMatch [array<string>]

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

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))\\.[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

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
    },
    ...
    ],
    "perfStats": {
      "start": epoch,
      "end": 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.

Example:

Sort test path alphabetically.

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 / options.shardCount);
    const shardStart = shardSize * (options.shardIndex - 1);
    const shardEnd = shardSize * options.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/facebook/jest/blob/6b8b1404a1d9254e7d5d90a8934087a9c9899dab/packages/jest-runner/src/types.ts#L17-L21
    const copyTests = Array.from(tests);
    return copyTests.sort((testA, testB) => (testA.path > testB.path ? 1 : -1));
  }
}

module.exports = CustomSequencer;

Use it in your Jest config file like this:

{
  "testSequencer": "path/to/testSequencer.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.

"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:

{
  "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.

Example:

{
  "transformIgnorePatterns": [
    "<rootDir>/bower_components/",
    "<rootDir>/node_modules/"
  ]
}

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/lo-dash, 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

Indicates whether each individual test should be reported during the run. All errors will also still be shown on the bottom after execution. Note that if there is only one test file being run it will default to true.

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). 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.

Example:

{
  "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:

• jest-watch-master
• jest-watch-select-projects
• jest-watch-suspend
• jest-watch-typeahead
• jest-watch-yarn-workspaces

watchman [boolean]

Default: true

Whether to use watchman for file crawling.

// [string]

No default

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

Example:

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