Jest is a JavaScript testing framework designed to ensure correctness of any JavaScript codebase. It allows you to write tests with an approachable, familiar and feature-rich API that …

There are two ways to have Jest global APIs typed for test files written in TypeScript. You can use type definitions which ships with Jest and will update each time you update Jest.

See React: Function and Class Components. Reminders that with Class components, we expect Jest to be used to test props and not methods directly. Now let's use React's test renderer and …

Jest is a universal testing platform, with the ability to adapt to any JavaScript library or framework. In this section, we'd like to link to community posts and articles about integrating Jest into …

Now, in order to test this method without actually hitting the API (and thus creating slow and fragile tests), we can use the jest.mock(...) function to automatically mock the axios module.

Jun 4, 2025 · Jest has been the most popular JavaScript testing framework for a decade. It is used by millions of developers, supporting a wide range of projects from small libraries to the …

Jest has default serializers for built-in JavaScript types, HTML elements (Jest 20.0.0+), ImmutableJS (Jest 20.0.0+) and for React elements. See snapshot test tutorial for more …

Jun 10, 2025 · If you'd like to learn how to build a testing framework like Jest from scratch, check out this video: There is also a written guide you can follow. It teaches the fundamental …

The Jest repository contains many examples of testing the output of Jest itself, the output of Jest's assertion library as well as log messages from various parts of the Jest codebase.

You can use that in your configuration to conditionally setup only the compilation needed for Jest, e.g. // You can use isTest to determine what presets and plugins to use.