Limits of Vite preview mode for testing integrations without production credentials

Goal: Use Vite's preview server to run integration tests that do not require production credentials, relying on the built assets.

Constraint: The preview server serves only static files from the dist directory and does not read .env files at runtime; environment variables must be baked into the build, and any server‑side logic or middleware is unavailable.

Uncertainty: Whether preview can faithfully represent runtime behavior when the application depends on dynamic env values or server‑side features, and what alternatives exist for testing those parts.

1. Can preview be considered a valid test environment for integrations that need runtime VITE_ variables?
2. If runtime env vars are required, what is the recommended approach to simulate them without altering the build?
3. Does the lack of dev‑server middleware in preview affect tests that rely on API mocking or SSR, and how should those be handled?