Vitest Testing

Setting up Vitest testing with jsdom requires a vitest.config.ts file with the environment set to jsdom and a setup file. This configuration provides the DOM APIs required by Testing Library to render and assert React components.

The best way to mock fetch and timers in Vitest is using vi.mock for global.fetch and fake timers. These mocking APIs isolate units and external dependencies, ensuring deterministic test outcomes without waiting for real network or delay.

Use vi.fn to create mock functions and vi.spyOn to track or override existing module methods in Vitest. These APIs isolate external dependencies and verify interactions, ensuring tests focus purely on the target logic.

Vitest works seamlessly with Testing Library for React component testing, providing guidance on async flows and user-event interactions. This combination validates UI behavior and API error handling within jsdom environments.

Test coverage reporting in a Vite project is enabled by configuring coverage options in your vitest.config.ts file. Vitest generates reports validating business logic and UI behavior before CI runs.

Slow or flaky Vitest unit tests often result from unmocked network calls or real timers. Utilizing vi.mock for global.fetch and fake timers isolates units, removing external dependencies to ensure fast, deterministic feedback loops.