The @jest/globals package provides access to Jest's global variables and functions, making it easier to write tests by providing a consistent testing environment. This package is particularly useful when working with ES modules, where Jest's globals are not automatically available. It includes functionalities such as test definition, mocking, and assertions.

What are @jest/globals's main functionalities?

Defining tests

Allows the definition of test cases. The `test` function is used to define a block of code that tests a specific part of your application. The `expect` function is used to make an assertion about a particular value.

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

test('adds 1 + 2 to equal 3', () => {
  expect(1 + 2).toBe(3);
});

Mocking functions

Enables the mocking of functions, allowing you to simulate the behavior of your code's dependencies. This is useful for isolating the code under test and controlling its environment.

import { jest } from '@jest/globals';

const mockFn = jest.fn();
mockFn.mockReturnValue('mocked value');

expect(mockFn()).toBe('mocked value');

Grouping tests

Provides a way to group related tests using the `describe` function. This helps in organizing tests, especially when testing complex applications.

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

describe('math operations', () => {
  test('adds 1 + 2 to equal 3', () => {
    expect(1 + 2).toBe(3);
  });

  test('subtracts 2 - 1 to equal 1', () => {
    expect(2 - 1).toBe(1);
  });
});

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Changelog

Source

26.0.0

Features

[jest-environment-jsdom] [BREAKING] Upgrade jsdom to v16 (#9606)
[@jest/fake-timers] Add possibility to use a modern implementation of fake timers, backed by @sinonjs/fake-timers (#7776)
[jest-runtime] Add createMockFromModule as an alias for genMockFromModule (#9962)

Fixes

[babel-jest] Handle null being passed to createTransformer (#9955)
[jest-circus, jest-console, jest-jasmine2, jest-reporters, jest-util, pretty-format] Fix time durating formatting and consolidate time formatting code (#9765)
[jest-circus] [BREAKING] Fail tests if a test takes a done callback and have return values (#9129)
[jest-circus] [BREAKING] Throw a proper error if a test / hook is defined asynchronously (#8096)
[jest-circus] Throw more descriptive error if hook is defined inside test (#9957)
[jest-circus] [BREAKING] Align execution order of tests to match jasmine's top to bottom order (#9965)
[jest-config, jest-resolve] [BREAKING] Remove support for browser field (#9943)
[jest-haste-map] Stop reporting files as changed when they are only accessed (#7347)
[jest-resolve] Show relative path from root dir for module not found errors (#9963)
[jest-runtime] Fix absolute path moduleNameMapper + jest.mock bug (#8727)

Chore & Maintenance

[*] [BREAKING] TypeScript definitions requires a minimum of TypeScript v3.8 (#9823)
[*] [BREAKING] Drop support for Node 8 (#9423)
[*] Upgrade to chalk@4 (#9752)
[*] Remove usage of realpath-native (#9952)
[docs] Fix example reference implementation to use Jest with Phabricator (#8662)
[docs] Added default compiler to transform (#8583)
[docs] Updated Testing Frameworks guide with React; make it generic (#9106)
[expect, jest-mock, pretty-format] [BREAKING] Remove build-es5 from package (#9945)
[@jest/fake-timers, @jest/environment] [BREAKING] Rename LolexFakeTimers to ModernFakeTimers (#9960)
[jest-haste-map] [BREAKING] removed providesModuleNodeModules (#8535)
[jest-runtime] [BREAKING] Remove long-deprecated require.requireActual and require.requireMock methods (#9854)

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Last updated on 04 May 2020

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