jest-mock
Advanced tools
Package description
The jest-mock package is a module for mocking classes and objects in JavaScript tests. It is part of the Jest testing framework but can be used independently. It allows developers to create mock functions, spy on function calls, and set return values or implementations for testing purposes.
Creating Mock Functions
This feature allows you to create a mock function that can track calls, arguments, and return values. It can be used to test how a function is used without actually executing its logic.
const mockFn = jest.fn();Mocking Return Values
With this feature, you can set a default return value for a mock function. This is useful when you want to test the behavior of code that depends on the return value of the function being mocked.
const mockFn = jest.fn().mockReturnValue('default value');Mocking Modules
This feature allows you to mock entire modules, which is particularly useful when you want to isolate the module being tested from its dependencies.
jest.mock('moduleName', () => { return jest.fn(() => 'mocked module') });Spying on Methods
Spying on methods enables you to observe and track calls to object methods without affecting their actual implementation. This is useful for verifying that methods are called with the correct arguments.
const spy = jest.spyOn(object, 'methodName');Sinon is a standalone test spies, stubs, and mocks library for JavaScript. It provides similar functionalities to jest-mock, such as spying on functions, creating stubs, and mocking objects. Sinon can be used with any testing framework and is not tied to Jest.
Proxyquire is a tool for mocking modules in Node.js. It allows you to override dependencies during testing, which is similar to jest-mock's module mocking capabilities. However, proxyquire focuses specifically on Node.js module system and does not provide function mocking or spying.
Testdouble.js (td.js) is a minimal test double library for TDD with JavaScript. It provides a similar API to jest-mock for creating test doubles like stubs, mocks, and spies. Testdouble.js aims to have a simpler and more expressive syntax compared to other mocking libraries.
Changelog
jest 20.0.0
--projects option to run one instance of Jest in multiple projects at the same time. (#3400)expect matchers through .resolves and .rejects. (#3068)expect.hasAssertions() function similar to expect.assertions(). (#3379)this.equals function exposed to custom matchers. (#3469)valid-expect lint rule in eslint-plugin-jest. (#3067)@jest-environment in the docblock. (#2859)reporters in the configuration. (#3349)jest-editor-support into a separate jest-test-typescript-parser package. (#2973)babel-jest to look up the babel field in package.json as a fallback.jest-editor-support's parser to not crash on incomplete ASTs. (#3259)jest-resolve to use is-builtin-module instead of resolve.isCore. (#2997)jest-snapshot to normalize line endings in the serialize function. (#3002)--silent flag. (#3003)notify option not taking precedence over config option. (#3340)jest-editor-support. (#3344)undefined. (#3354)expect. (#3306)expect.assertions error. (#3033)jest-file-exists. (#3105)Config type. (#3366)jest-file-exists. (#3101)FAQs
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We found that jest-mock demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago. It has 3 open source maintainers collaborating on the project.
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