@vitest/expect
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Package description
The @vitest/expect package is a part of the Vitest testing framework, designed to work seamlessly with its ecosystem. It provides a powerful expectation library that allows developers to write assertions for their tests. This package is particularly useful for unit and integration testing, offering a wide range of matchers and utilities to test the behavior of JavaScript code.
Basic Expectations
Allows for basic equality checks, useful for asserting that a value matches an expected result.
expect(value).toBe(42);Object and Array Matching
Enables deep equality checks for objects and arrays, as well as checking for the presence of an item in an array.
expect(object).toEqual({ key: 'value' });
expect(array).toContain(item);Asynchronous Testing
Facilitates testing of asynchronous operations, allowing assertions on resolved values of promises.
await expect(Promise.resolve('value')).resolves.toBe('value');Mocking and Spies
Supports the creation of mock functions and spies, enabling the testing of function calls and their arguments.
const mockFunction = vi.fn();
expect(mockFunction).toHaveBeenCalledTimes(1);Jest is a well-known testing framework that includes its own expectation library, very similar to @vitest/expect. It offers a comprehensive suite of features for testing JavaScript code, including snapshot testing, global setup/teardown, and more. Compared to @vitest/expect, Jest is more established but also heavier, making @vitest/expect a lighter alternative for projects already using Vitest.
Chai is an assertion library for node and the browser that can be paired with any testing framework. It offers a range of interfaces (expect, should, assert) that allow developers to write tests in a style that suits them best. Compared to @vitest/expect, Chai is more flexible in terms of integration but does not offer the same level of integration with the Vitest ecosystem.
The expect package is another assertion library that provides a set of extensive matchers to write tests. It is lightweight and does not tie itself to a specific test runner. While it shares similar functionalities with @vitest/expect, it lacks the tight integration and specific optimizations for the Vitest environment.
Readme
Jest's expect matchers as a Chai plugin.
import * as chai from 'chai'
import { JestAsymmetricMatchers, JestChaiExpect, JestExtend } from '@vitest/expect'
// allows using expect.extend instead of chai.use to extend plugins
chai.use(JestExtend)
// adds all jest matchers to expect
chai.use(JestChaiExpect)
// adds asymmetric matchers like stringContaining, objectContaining
chai.use(JestAsymmetricMatchers)
FAQs
Jest's expect matchers as a Chai plugin
The npm package @vitest/expect receives a total of 3,453,805 weekly downloads. As such, @vitest/expect popularity was classified as popular.
We found that @vitest/expect demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago. It has 4 open source maintainers collaborating on the project.
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