jest-matcher-utils

What is jest-matcher-utils?

The jest-matcher-utils package provides utility functions for creating custom Jest matchers. It is designed to help developers write their own matchers that integrate seamlessly with Jest's built-in expectation system, offering a way to extend Jest's assertion capabilities with custom logic. The utilities provided by this package include formatting values for error messages, comparing values, and generating matcher error messages.

What are jest-matcher-utils's main functionalities?

pretty-format

Formats any JavaScript value for pretty printing, which is useful for generating readable error messages in custom matchers.

const { prettyFormat } = require('jest-matcher-utils');
console.log(prettyFormat({ foo: 'bar' }));

matcherHint

Generates a hint string for a matcher, which can be used at the beginning of error messages to indicate which matcher failed.

const { matcherHint } = require('jest-matcher-utils');
console.log(matcherHint('.toBe'));

printExpected and printReceived

These functions format the expected and received values to be included in error messages, applying color highlighting to improve readability.

const { printExpected, printReceived } = require('jest-matcher-utils');
console.log(`Expected: ${printExpected(true)}
Received: ${printReceived(false)}`);

Other packages similar to jest-matcher-utils

chai

Chai is a BDD / TDD assertion library for node and the browser that can be delightfully paired with any javascript testing framework. It offers similar functionality to jest-matcher-utils in the sense that it provides a rich set of assertions and plugins to extend its capabilities. However, Chai is a standalone assertion library, not tied to any specific test runner like Jest.

expect

Expect is a minimalist assertion library that comes with Jest but can also be used independently. It provides a similar API for writing test assertions as jest-matcher-utils, but jest-matcher-utils focuses more on the utilities for creating custom matchers rather than providing a comprehensive set of built-in matchers.

README

The README file is missing

Changelog

23.6.0

Features

• [jest-cli] Add changedSince to allowed watch mode configs (#6955)
• [babel-jest] Add support for babel.config.js added in Babel 7.0.0 (#6911)
• [jest-resolve] Add support for an experimental mapper option (Watchman crawler only) that adds virtual files to the Haste map (#6940)

Fixes

• [jest-resolve] Only resolve realpath once in try-catch (#6925)
• [expect] Fix TypeError in toBeInstanceOf on null or undefined (#6912)
• [jest-jasmine2] Throw a descriptive error if the first argument supplied to a hook was not a function (#6917) and (#6931)
• [jest-circus] Throw a descriptive error if the first argument supplied to a hook was not a function (#6917) and (#6931)
• [expect] Fix variadic custom asymmetric matchers (#6898)
• [jest-cli] Fix incorrect testEnvironmentOptions warning (#6852)
• [jest-each] Prevent done callback being supplied to describe (#6843)
• [jest-config] Better error message for a case when a preset module was found, but no jest-preset.js or jest-preset.json at the root (#6863)
• [jest-haste-map] Catch crawler error when unsuccessfully reading directories (#6761)

Chore & Maintenance

• [docs] Add custom toMatchSnapshot matcher docs (#6837)
• [docs] Improve the documentation regarding preset configuration (#6864)
• [docs] Clarify usage of --projects CLI option (#6872)
• [docs] Correct failure-change notification mode (#6878)
• [scripts] Don’t remove node_modules from subdirectories of presets in e2e tests (#6948)
• [diff-sequences] Double-check number of differences in tests (#6953)