Vitest best practices

Use when writing, reviewing, or debugging tests with Vitest.

Mental model

• Vitest is a Vite-powered test runner. Its configuration and module behavior are closely tied to Vite’s transform pipeline.
• Keep tests aligned with the runtime they simulate: node, jsdom, happy-dom, or browser mode.
• Treat test setup as part of the architecture surface, not as disposable glue code.

Config and structure

• Prefer a single clear config path. If the project already has vite.config.*, keep Vitest config integrated there unless the repo has a documented reason to split it out.
• If a separate vitest.config.* exists, make sure it intentionally mirrors or merges the Vite settings the tests depend on.
• Keep setup files, aliases, and environment assumptions explicit so failures are reproducible.

Running tests