Jest

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Configuring Jest

Jest's configuration can be defined in the package.json file of your project, through a jest.config.js file or through the --config <path/to/js|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:

// jest.config.js
module.exports = {
  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": true,
  "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.

Reference #

automock [boolean] #

Default: false

This option is disabled by default. If you are introducing Jest to a large organization with an existing codebase but few tests, enabling this option can be helpful to introduce unit tests gradually. Modules can be explicitly auto-mocked using jest.mock(moduleName).

Note: Core modules, like fs, are not mocked by default. They can be mocked explicitly, like jest.mock('fs').

Note: Automocking has a performance cost most noticeable in large projects. See here for details and a workaround.

browser [boolean] #

Default: false

Respect Browserify's "browser" field in package.json when resolving modules. Some modules export different versions based on whether they are operating in Node or a browser.

bail [boolean] #

Default: false

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 the first failure.

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 raking that needs to happen while running tests. This config option lets you customize where Jest stores that cache data on disk.

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/**.

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

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/"].

coverageReporters [array<string>] #

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

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

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

coverageThreshold [object] #

Default: undefined

This will be used to configure minimum threshold enforcement for coverage results. If the thresholds are not met, jest will return failure. Thresholds, when specified as a positive number are taken to be the minimum percentage required. When a threshold is specified as a negative number it represents the maximum number of uncovered entities allowed.

For example, statements: 90 implies minimum statement coverage is 90%. statements: -10 implies that no more than 10 uncovered statements are allowed.

{
  ...
  "jest": {
    "coverageThreshold": {
      "global": {
        "branches": 50,
        "functions": 50,
        "lines": 50,
        "statements": 50
      }
    }
  }
}

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.

mapCoverage [boolean] #

available in Jest 20.0.0+ #

Default: false

If you have transformers configured that emit source maps, Jest will use them to try and map code coverage against the original source code when writing reports and checking thresholds. This is done on a best-effort basis as some compile-to-JavaScript languages may provide more accurate source maps than others. This can also be resource-intensive. If Jest is taking a long time to calculate coverage at the end of a test run, try setting this option to false.

Both inline source maps and source maps returned directly from a transformer are supported. Source map URLs are not supported because Jest may not be able to locate them. To return source maps from a transformer, the process function can return an object like the following. The map property may either be the source map object, or the source map object as a JSON string.

return {
  code: 'the code',
  map: 'the source map',
};

moduleFileExtensions [array<string>] #

Default: ["js", "json", "jsx", "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.

If you are using TypeScript this should be ["js", "jsx", "json", "ts", "tsx"]

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"]

moduleNameMapper [object<string, string>] #

Default: null

A map from regular expressions to 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"
  }
}

Note: If you provide module name 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. 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.

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 exports a jest-preset.json module on its top level.

projects [array<string>] #

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.

clearMocks [boolean] #

Default: false

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

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

Default: undefined

available in Jest 20.0.0+ #

Use this configuration option to add custom reporters to Jest. A custom reporter is a class that implements onRunStart, onTestStart, onTestResult, onRunComplete methods that will be called when any of those events occurs.

If custom reporters are specified, the default Jest reporters will be overridden. To keep default reporters, default can be passed as a module name.

This will override default reporters:

{
  "reporters": [
    "<rootDir>/my-custom-reporter.js"
  ]
}

This will use custom reporter in addition to default reporters that Jest provides:

{
  "reporters": [
    "default",
    "<rootDir>/my-custom-reporter.js"
  ]
}

Additionally, custom reporters can be configured by passing an options object as a second argument:

{
  "reporters": [
    "default",
    ["<rootDir>/my-custom-reporter.js", {"banana": "yes", "pineapple": "no"}]
  ]
}

Custom reporter modules must define a class that takes a GlobalConfig and reporter options as constructor arguments:

Example reporter:

// my-custom-reporter.js
class MyCustomReporter {
  constructor(globalConfig, options) {
    this._globalConfig = globalConfig;
    this._options = options;
  }

  onRunComplete(contexts, results) {
    console.log('Custom reporter output:');
    console.log('GlobalConfig: ', this._globalConfig);
    console.log('Options: ', this._options);
  }
}

module.exports = MyCustomReporter;

Custom reporters can also force Jest to exit with non-0 code by returning an Error from getLastError() methods

class MyCustomReporter {
  // ...
  getLastError() {
    if (this._shouldFail) {
      return new Error('my-custom-reporter.js reported an error');
    }
  }
}

For the full list of methods and argument types see Reporter type in types/TestRunner.js

resetMocks [boolean] #

Default: false

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

resetModules [boolean] #

Default: false

If enabled, the module registry for every test file will be reset before running each individual test. This is useful to isolate modules for every test so that local module state doesn't conflict between tests. This can be done programmatically using jest.resetModules().

resolver [string] #

Default: undefined

available in Jest 20.0.0+ #

This option allows the use of a custom resolver. This resolver must be a node module that exports a function expecting a string as the first argument for the path to resolve and an object with the following structure as the second argument:

{
  "basedir": string,
  "browser": bool,
  "extensions": [string],
  "moduleDirectory": [string],
  "paths": [string]
}

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.

rootDir [string] #

Default: The root of the directory containing 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.

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

setupFiles [array] #

Default: []

The paths to modules that run some code to configure or set up the testing environment before each test. Since every test runs in its own environment, these scripts will be executed in the testing environment immediately before executing the test code itself.

It's worth noting that this code will execute before setupTestFrameworkScriptFile.

setupTestFrameworkScriptFile [string] #

Default: undefined

The path to a module that runs some code to configure or set up the testing framework before each test. 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.

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 this module.

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 = {
  print(val, serialize, indent) {
    return 'Pretty foo: ' + serialize(val.foo);
  },

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

};

serialize 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.

testEnvironment [string] #

Default: "jsdom"

The test environment that will be used for testing. The default environment in Jest is a browser-like environment through jsdom. If you are building a node service, you can use the node option to use a node-like environment instead.

If some tests require another environment, you can add a @jest-environment docblock.

available in Jest 20.0.0+ #
/**
 * @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 runScript and dispose methods. See the node or jsdom environments as examples.

testMatch [array<string>] #

available in Jest 19.0.0+ #

(default: [ '**/__tests__/**/*.js?(x)', '**/?(*.)(spec|test).js?(x)' ])

The glob patterns Jest uses to detect test files. By default it looks for .js and .jsx 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], 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] #

Default: (/__tests__/.*|(\\.|/)(test|spec))\\.jsx?$

The pattern Jest uses to detect test files. By default it looks for .js and .jsx 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:

{
  "success": bool,
  "startTime": epoch,
  "numTotalTestSuites": number,
  "numPassedTestSuites": number,
  "numFailedTestSuites": number,
  "numRuntimeErrorTestSuites": number,
  "numTotalTests": number,
  "numPassedTests": number,
  "numFailedTests": number,
  "numPendingTests": number,
  "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
    },
    ...
    ],
    "perfStats": {
      "start": epoch,
      "end": epoch
    },
    "testFilePath": absolute path to test file,
    "coverage": {}
  },
  ...
  ]
}

testRunner [string] #

Default: jasmine2

This option allows use of a custom test runner. The default is jasmine2. 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(
  config: Config,
  environment: Environment,
  runtime: Runtime,
  testPath: string,
): Promise<TestResult>

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

testURL [string] #

Default: about:blank

This option sets the URL for the jsdom environment. It is reflected in properties such as location.href.

timers [string] #

Default: real

Setting this value to fake allows the use of fake timers for functions such as setTimeout. Fake timers are useful when a piece of code sets a long timeout that we don't want to wait for in a test.

transform [object<string, string>] #

Default: undefined

A map from regular expressions to paths to transformers. A transformer is a module that provides a synchronous function for transforming source files. For example, if you wanted to be able to use a new language feature in your modules or tests that isn't yet supported by node, you might plug in one of many compilers that compile a future version of JavaScript to a current one. Example: see the examples/typescript example or the webpack tutorial.

Examples of such compilers include babel, typescript, and async-to-gen.

Note: a transformer is only ran once per file unless the file has changed. During development of a transformer it can be useful to run Jest with --no-cache or to frequently delete Jest's cache.

Note: if you are using the babel-jest transformer and want to use an additional code preprocessor, keep in mind that when "transform" is overwritten in any way the babel-jest is not loaded automatically anymore. If you want to use it to compile JavaScript code it has to be explicitly defined. See babel-jest plugin

transformIgnorePatterns [array<string>] #

Default: ["/node_modules/"]

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

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>/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.

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