expect
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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
29.0.0
[expect] [BREAKING] Differentiate between MatcherContext MatcherUtils and MatcherState types (#13141)[jest-circus] Add support for test.failing.each (#13142)[jest-config] [BREAKING] Make snapshotFormat default to escapeString: false and printBasicPrototype: false (#13036)[jest-config] [BREAKING] Remove undocumented collectCoverageOnlyFrom option (#13156)[jest-environment-jsdom] [BREAKING] Upgrade to jsdom@20 (#13037, #13058)[@jest/globals] Add jest.Mocked, jest.MockedClass, jest.MockedFunction and jest.MockedObject utility types (#12727)[jest-mock] [BREAKING] Refactor Mocked* utility types. MaybeMockedDeep and MaybeMocked became Mocked and MockedShallow respectively; only deep mocked variants of MockedClass, MockedFunction and MockedObject are exported (#13123, #13124)[jest-mock] [BREAKING] Change the default jest.mocked helper’s behavior to deep mocked (#13125)[jest-snapshot] [BREAKING] Let babel find config when updating inline snapshots (#13150)[@jest/test-result, @jest/types] [BREAKING] Replace Bytes and Milliseconds types with number (#13155)[jest-worker] Adds workerIdleMemoryLimit option which is used as a check for worker memory leaks >= Node 16.11.0 and recycles child workers as required (#13056, #13105, #13106, #13107)[pretty-format] [BREAKING] Remove ConvertAnsi plugin in favour of jest-serializer-ansi-escapes (#13040)[pretty-format] Allow to opt out from sorting object keys with compareKeys: null (#12443)[jest-config] Fix testing multiple projects with TypeScript config files (#13099)[@jest/expect-utils] Fix deep equality of ImmutableJS Record (#13055)[jest-haste-map] Increase the maximum possible file size that jest-haste-map can handle (#13094)[jest-runtime] Properly support CJS re-exports from dual packages (#13170)[jest-snapshot] Make prettierPath optional in SnapshotState (#13149)[jest-snapshot] Fix parsing error from inline snapshot files with JSX (#12760)[jest-worker] When a process runs out of memory worker exits correctly and doesn't spin indefinitely (#13054)[*] [BREAKING] Drop support for Node v12 and v17 (#13033)[docs] Fix webpack name (#13049)[docs] Explicit how to set n for --bail (#13128)[docs] Update Enzyme URL (#13166)[jest-leak-detector] Remove support for weak-napi (#13035)[jest-snapshot] [BREAKING] Require rootDir as argument to SnapshotState (#13150)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).
The npm package expect receives a total of 25,224,426 weekly downloads. As such, expect popularity was classified as popular.
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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