@jest/globals

What is @jest/globals?

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);
  });
});

Other packages similar to @jest/globals

mocha

Mocha is a feature-rich JavaScript test framework running on Node.js and in the browser, making asynchronous testing simple. It's similar to @jest/globals in providing a testing structure (describe and it blocks), but it requires additional libraries like Chai for assertions and Sinon for spies, mocks, and stubs.

chai

Chai is a BDD / TDD assertion library for node and the browser that can be delightfully paired with any javascript testing framework. It's similar to the assertion part of @jest/globals, offering a range of assertions via expect, should, and assert interfaces. However, it does not provide test runner or mocking capabilities.

sinon

Sinon provides standalone test spies, stubs, and mocks for JavaScript. Works with any unit testing framework. It's similar to the mocking functionality of @jest/globals but is focused solely on the aspect of mocking, without an integrated test runner or assertion library.

README

The README file is missing

Changelog

29.7.0

Features

• [create-jest] Add npm init / yarn create initialiser for Jest projects (#14465)
• [jest-validate] Allow deprecation warnings for unknown options (#14499)

Fixes

• [jest-resolver] Replace unmatched capture groups in moduleNameMapper with empty string instead of undefined (#14507)
• [jest-snapshot] Allow for strings as well as template literals in inline snapshots (#14465)
• [@jest/test-sequencer] Calculate test runtime if perStats.duration is missing (#14473)

Performance

• [@jest/create-cache-key-function] Cache access of NODE_ENV and BABEL_ENV (#14455)

Chore & Maintenance

• [jest-cli] Move internal config initialisation logic to the create-jest package (#14465)