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/en/expect.html).
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.
This package exports the expect function used in Jest. You can find its documentation on Jest's website.
24.9.0
[expect] Highlight substring differences when matcher fails, part 1 (#8448)[expect] Highlight substring differences when matcher fails, part 2 (#8528)[expect] Improve report when mock-spy matcher fails, part 1 (#8640)[expect] Improve report when mock-spy matcher fails, part 2 (#8649)[expect] Improve report when mock-spy matcher fails, part 3 (#8697)[expect] Improve report when mock-spy matcher fails, part 4 (#8710)[expect] Throw matcher error when received cannot be jasmine spy (#8747)[expect] Improve report when negative CalledWith assertion fails (#8755)[expect] Improve report when positive CalledWith assertion fails (#8771)[expect] Display equal values for ReturnedWith similar to CalledWith (#8791)[expect, jest-snapshot] Change color from green for some args in matcher hints (#8812)[jest-snapshot] Highlight substring differences when matcher fails, part 3 (#8569)[jest-core] Improve report when snapshots are obsolete (#8665)[jest-cli] Improve chai support (with detailed output, to match jest exceptions) (#8454)[*] Manage the global timeout with --testTimeout command line argument. (#8456)[pretty-format] Render custom displayName of memoized components (#8546)[jest-validate] Allow maxWorkers as part of the jest.config.js (#8565)[jest-runtime] Allow passing configuration objects to transformers (#7288)[@jest/core, @jest/test-sequencer] Support async sort in custom testSequencer (#8642)[jest-runtime, @jest/fake-timers] Add jest.advanceTimersToNextTimer (#8713)[@jest-transform] Extract transforming require logic within jest-core into @jest-transform (#8756)[jest-matcher-utils] Add color options to matcherHint (#8795)[jest-circus/jest-jasmine2] Give clearer output for Node assert errors (#8792)[jest-runner] Export all types in the type signature of jest-runner (#8825)[jest-cli] Detect side-effect only imports when running --onlyChanged or --changedSince (#8670)[jest-cli] Allow --maxWorkers to work with % input again (#8565)[babel-plugin-jest-hoist] Expand list of whitelisted globals in global mocks (#8429)[jest-core] Make watch plugin initialization errors look nice (#8422)[jest-snapshot] Prevent inline snapshots from drifting when inline snapshots are updated (#8492)[jest-haste-map] Don't throw on missing mapper in Node crawler (#8558)[jest-core] Fix incorrect passWithNoTests warning (#8595)[jest-snapshots] Fix test retries that contain snapshots (#8629)[jest-mock] Fix incorrect assignments when restoring mocks in instances where they originally didn't exist (#8631)[expect] Fix stack overflow when matching objects with circular references (#8687)[jest-haste-map] Workaround a node >=12.5.0 bug that causes the process not to exit after tests have completed and cancerous memory growth (#8787)[docs] Replace FlowType with TypeScript in CONTRIBUTING.MD code conventions[jest-leak-detector] remove code repeat (#8438)[docs] Add example to jest.requireActual (#8482)[docs] Add example to jest.mock for mocking ES6 modules with the factory parameter (#8550)[docs] Add information about using jest.doMock with ES6 imports (#8573)[docs] Fix variable name in custom-matcher-api code example (#8582)[docs] Fix example used in custom environment docs (#8617)[docs] Updated react tutorial to refer to new package of react-testing-library (@testing-library/react) (#8753)[docs] Updated imports of react-testing-library to @testing-library/react in website (#8757)[jest-core] Add getVersion (moved from jest-cli) (#8706)[docs] Fix MockFunctions example that was using toContain instead of toContainEqual (#8765)[*] Make sure copyright header comment includes license (#8783)[*] Check copyright and license as one joined substring (#8815)[docs] Fix WatchPlugins jestHooks.shouldRunTestSuite example that receives an object (#8784)[*] Enforce LF line endings (#8809)[pretty-format] Delete obsolete link and simplify structure in README (#8824)[docs] Fix broken transform link on webpack page (#9155)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 18,158,643 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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