javascript-testing-patterns

To set up Jest or Vitest for TypeScript, you need to configure the testing framework to parse TypeScript syntax, typically using ts-jest for Jest or native TypeScript support in Vitest. The skill provides configuration guides to initialize your test environment and ensure your compiler options align with your testing setup.

The best way to mock modules in JavaScript testing involves using framework-specific functions like Jest's jest.mock or Vitest's vi.mock to replace module implementations. This skill demonstrates mocking techniques including module replacement, dependency injection, and spying on function calls to isolate code units.

Yes, Testing Library is specifically designed for frontend testing and works effectively with React components and custom hooks. The skill provides practical examples for rendering components, querying DOM nodes, and testing asynchronous hook behavior to ensure UI reliability.

Implementing test-driven development (TDD) involves writing failing tests before implementation, then writing code to pass those tests, and finally refactoring. This skill covers TDD patterns for complex features, guiding you through the red-green-refactor cycle using Jest or Vitest.

Fixtures are pre-configured data sets or setup states used to provide consistent inputs for integration testing in Vitest. They help by ensuring tests run against predictable data, reducing flakiness and isolating test scenarios, with examples provided for setting up and managing these test utilities.

Yes, this skill covers snapshot testing to capture and verify serialized component outputs, and coverage reporting to measure the percentage of code executed by your tests. It provides patterns for configuring these tools within Jest and Vitest environments.