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

jest-matcher-utils

This package's exports are most notably used by expect's this.utils.

Installation

To add this package as a dependency of a project, run either of the following commands:

• npm install jest-matcher-utils
• yarn add jest-matcher-utils

Exports (src/index.ts)

Functions

stringify highlightTrailingWhitespace printReceived printExpected printWithType ensureNoExpected ensureActualIsNumber ensureExpectedIsNumber ensureNumbers ensureExpectedIsNonNegativeInteger printDiffOrStringify diff pluralize getLabelPrinter matcherErrorMessage matcherHint

Types

MatcherHintOptions DiffOptions

Constants

EXPECTED_COLOR RECEIVED_COLOR INVERTED_COLOR BOLD_WEIGHT DIM_COLOR SUGGEST_TO_CONTAIN_EQUAL SERIALIZABLE_PROPERTIES