jest-matcher-utils
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Package description
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.
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)}`);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 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.
Changelog
jest 15.0.0
.spec.js and .test.js as test files.--env option to override the default test environment.--watchAll, made --watch interactive and added the ability to update snapshots and select test patterns in watch mode.testEnvironment resolution to prefer jest-environment-{name} instead of {name} only. This prevents a module collision when using jsdom as test environment.moduleNameMapper now uses a resolution algorithm.global.global to the node environment.mock.collectCoverageFrom to collect code coverage from untested files.FAQs
A set of utility functions for expect and related packages
We found that jest-matcher-utils demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago. It has 6 open source maintainers collaborating on the project.
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