jest-testing

Jest configuration involves setting up environments, presets, and file patterns for your project type. For React projects, use the appropriate preset; for Node.js, configure the environment and module resolution. The Skill provides guidance on setup steps, environment variables, and preset selection to match your stack.

Module mocking in Jest uses jest.mock() to replace dependencies with test doubles. The Skill covers built-in mocking strategies, custom matchers, and when to mock versus stubbing, helping you isolate units and control side effects in both React and Node.js tests.

Organize tests using describe blocks to group related cases, name files with .test.js or .test.ts extensions, and co-locate tests with source code. The Skill provides templates and best practices for test structure, coverage strategies, and baseline test scaffolding across project types.

Yes, Jest supports TypeScript through ts-jest and similar presets, and includes snapshot testing for React components and serialized output. The Skill covers snapshot configuration, coverage management, and TypeScript setup to validate component rendering and API responses reliably.

React Testing Library pairs with Jest to test components by querying the DOM and simulating user interactions. The Skill provides guidance on RTL matchers, component test organization, and mock strategies for props, state, and external dependencies in React applications.

Jest and Vitest share similar APIs but differ in configuration and performance characteristics. The Skill recognizes both and offers compatibility notes to help you understand trade-offs, migrate between tools, and apply Jest best practices to Vitest-based projects.