expect
Advanced tools
Package description
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.
Changelog
29.4.0
[expect, @jest/expect-utils] Support custom equality testers (#13654)[jest-config, jest-worker] Use os.availableParallelism if available to calculate number of workers to spawn (#13738)[@jest/globals, jest-mock] Add jest.replaceProperty() that replaces property value (#13496)[jest-haste-map] ignore Sapling vcs directories (.sl/) (#13674)[jest-resolve] Support subpath imports (#13705, #13723, #13777)[jest-runtime] Add jest.isolateModulesAsync for scoped module initialization of asynchronous functions (#13680)[jest-runtime] Add jest.isEnvironmentTornDown function (#13741)[jest-test-result] Added skipped and focused status to FormattedTestResult (#13700)[jest-transform] Support for asynchronous createTransformer (#13762)[jest-environment-node] Fix non-configurable globals (#13687)[@jest/expect-utils] toMatchObject should handle Symbol properties (#13639)[jest-mock] Fix mockReset and resetAllMocks undefined return value(#13692)[jest-resolve] Add global paths to require.resolve.paths (#13633)[jest-resolve] Correct node core module detection when using node: specifiers (#13806)[jest-runtime] Support WASM files that import JS resources (#13608)[jest-runtime] Use the scriptTransformer cache in jest-runner (#13735)[jest-runtime] Enforce import assertions when importing JSON in ESM (#12755 & #13805)[jest-snapshot] Make sure to import babel outside of the sandbox (#13694)[jest-transform] Ensure the correct configuration is passed to preprocessors specified multiple times in the transform option (#13770)Readme
This package exports the expect function used in Jest. You can find its documentation on Jest's website.
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).
We found that expect demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago. It has 2 open source maintainers collaborating on the project.
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