The 'expect' npm package is a library for writing test assertions. It is commonly used in conjunction with testing frameworks like Jest or Mocha to validate the behavior of JavaScript code. It provides a range of assertion types and matchers that allow developers to write expressive and readable tests.
Basic Assertions
This feature allows you to assert that a value matches exactly what you expect. The 'toBe' matcher compares with ===.
expect(2 + 2).toBe(4);Object Property Assertions
With this feature, you can assert that an object has a specific property with a certain value. The 'toHaveProperty' matcher checks for the existence and value of a property in an object.
expect({ name: 'Alice', age: 30 }).toHaveProperty('name', 'Alice');Exception Testing
This feature is used to test if a function throws an exception when it is executed. The 'toThrow' matcher is used to assert that an error is thrown with a specific message.
expect(() => { throw new Error('failure'); }).toThrow('failure');Array Containment
This feature allows you to assert that an array contains a specific item. The 'toContain' matcher checks if an array includes the expected item.
expect(['Alice', 'Bob', 'Eve']).toContain('Bob');Asynchronous Assertions
This feature enables you to write assertions for asynchronous code. The 'resolves' matcher waits for a promise to resolve and then checks the resolved value.
expect(Promise.resolve('success')).resolves.toBe('success');Chai is a BDD/TDD assertion library for node and the browser that can be paired with any javascript testing framework. It offers a similar range of matchers and assertions as expect, and it provides a fluent chainable language to construct assertions.
Should.js is an expressive, readable, framework-agnostic assertion library. The key difference is in the style of assertions it offers, using a more fluent chainable API that reads like English.
Assert is a module that provides a set of assertion functions for verifying invariants. It is built into Node.js and is less feature-rich compared to expect, but it serves as a simple way to write assertions in a Node.js environment.
Jest is a delightful JavaScript Testing Framework with a focus on simplicity. It comes with its own assertion library, which provides functionality similar to expect, as expect is actually part of Jest.
jest 22.0.5
[jest-leak-detector] Removed the reference to weak. Now, parent projects must install it by hand for the module to work.[expect] Fail test when the types of stringContaining and stringMatching matchers do not match. (#5069)[jest-cli] Treat dumb terminals as noninteractive (#5237)[jest-cli] jest --onlyChanged --changedFilesWithAncestor now also works with git. (#5189)[jest-config] fix unexpected condition to avoid infinite recursion in Windows platform. (#5161)[jest-config] Escape parentheses and other glob characters in rootDir before interpolating with testMatch. (#4838)[jest-regex-util] Fix breaking change in --testPathPattern (#5230)[expect] Do not override Error stack (with Error.captureStackTrace) for custom matchers. (#5162)[pretty-format] Pretty format for DOMStringMap and NamedNodeMap (#5233)[jest-cli] Use a better console-clearing string on Windows (#5251)[jest-jasmine] Allowed classes and functions as describe names. (#5154)[jest-jasmine2] Support generator functions as specs. (#5166)[jest-jasmine2] Allow spyOn with getters and setters. (#5107)[jest-config] Allow configuration objects inside projects array (#5176)[expect] Add support to .toHaveProperty matcher to accept the keyPath argument as an array of properties/indices. (#5220)[docs] Add documentation for .toHaveProperty matcher to accept the keyPath argument as an array of properties/indices. (#5220)[jest-runner] test environments are now passed a new options parameter. Currently this only has the console which is the test console that Jest will expose to tests. (#5223)[jest-environment-jsdom] pass the options.console to a custom instance of virtualConsole so jsdom is using the same console as the test. (#5223)FAQs
This package exports the `expect` function used in [Jest](https://jestjs.io/). You can find its documentation [on Jest's website](https://jestjs.io/docs/expect).
The npm package expect receives a total of 22,440,652 weekly downloads. As such, expect popularity was classified as popular.
We found that expect demonstrated a not healthy version release cadence and project activity because the last version was released a year ago. It has 2 open source maintainers collaborating on the project.
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