javascript-testing-patterns

Use async/await in your test functions and mock fetch or other async dependencies with vi.fn() or jest.fn(). Assert resolved values with expect and test rejections using expect().rejects.toThrow().

Vitest offers faster execution and native Vite integration with a Jest-compatible API, making it ideal for Vite-based projects. Jest remains a full-featured choice with broad ecosystem support, especially for older or non-Vite codebases.

Use vi.mock() with a factory function that returns mocked implementations of the module's exports. For example, mock nodemailer by returning an object whose createTransport returns a stubbed sendMail function.

Render the component with render(), query elements using semantic queries like getByRole or getByPlaceholderText, and simulate user interactions with fireEvent. Assert on rendered output and callback invocations rather than implementation details.

Use vi.useFakeTimers() to replace real timers, then call vi.advanceTimersByTime() to simulate time passing synchronously. Restore real timers with vi.useRealTimers() after the test to avoid side effects.

The configurations in this Skill set an 80% threshold for branches, functions, lines, and statements. This is a common baseline that catches most regressions without making tests brittle or slowing development.