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

jest 16.0.0

• Previously failed tests are now always run first.
• A new concurrent reporter shows currently running tests, a test summary, a progress bar and estimated remaining time if possible.
• Improved CLI colors.
• jest <pattern> is now case-insensitive.
• Added it.only, it.skip, test.only, test.skip and xtest.
• Added --testNamePattern=pattern or -t <pattern> to run individual tests in test files.
• Jest now warns for duplicate mock files.
• Pressing a, o, p, q or enter while tests are running in the watch mode, the test run will be interrupted.
• --bail now works together with --watch.
• Added test.concurrent for concurrent async tests.
• Jest now automatically considers files and tests with the .jsx extension.
• Added jest.clearAllMocks to clear all mocks manually.
• Rewrote Jest's snapshot implementation. jest-snapshot can now be more easily integrated into other test runners and used in other projects.
• This requires most snapshots to be updated when upgrading Jest.
• Objects and Arrays in snapshots are now printed with a trailing comma.
• Function names are not printed in snapshots any longer to reduce issues with code coverage instrumentation and different Node versions.
• Snapshots are now sorted using natural sort order.
• Snapshots are not marked as obsolete any longer when using fit or when an error is thrown in a test.
• Finished migration of Jasmine matchers to the new Jest matchers.
• Pretty print toHaveBeenLastCalledWith, toHaveBeenCalledWith, lastCalledWith and toBeCalledWith failure messages.
• Added toBeInstanceOf matcher.
• Added toContainEqual matcher.
• Added toThrowErrorMatchingSnapshot matcher.
• Improved moduleNameMapper resolution.
• Module registry fixes.
• Fixed invocation of the setupTestFrameworkScriptFile script to make it easier to use chai together with Jest.
• Removed react-native special case in Jest's configuration.
• Added --findRelatedTests <fileA> <fileB> cli option to run tests related to the specified files.
• Added jest.deepUnmock to babel-plugin-jest-hoist.
• Added jest.runTimersToTime which is useful together with fake timers.
• Improved automated mocks for ES modules compiled with babel.