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jest-matcher-utils
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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.
This package's exports are most notably used by expect
's this.utils
.
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
stringify
highlightTrailingWhitespace
printReceived
printExpected
printWithType
ensureNoExpected
ensureActualIsNumber
ensureExpectedIsNumber
ensureNumbers
ensureExpectedIsNonNegativeInteger
printDiffOrStringify
diff
pluralize
getLabelPrinter
matcherErrorMessage
matcherHint
MatcherHintOptions
DiffOptions
EXPECTED_COLOR
RECEIVED_COLOR
INVERTED_COLOR
BOLD_WEIGHT
DIM_COLOR
SUGGEST_TO_CONTAIN_EQUAL
SERIALIZABLE_PROPERTIES
30.0.5
[jest-config]
Allow testMatch
to take a string value[jest-worker]
Let workerIdleMemoryLimit
accept 0 to always restart worker child processes[expect]
Fix bigint
error (#15702)FAQs
A set of utility functions for expect and related packages
The npm package jest-matcher-utils receives a total of 44,659,742 weekly downloads. As such, jest-matcher-utils popularity was classified as popular.
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 5 open source maintainers collaborating on the project.
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