Can Remix route loader integration tests mock fetch without production credentials?

Goal: Verify that a Remix route loader integration test can replace live production credentials with mocked fetch or database calls while preserving server-side rendering behavior.

Constraint: Loaders execute on the server during the render phase and return serialized data to the client, so the test must account for server execution and client hydration without invoking real external services. Remix 2.0 changed loader execution order, so the target version may affect when mocks are invoked relative to rendering.

1. Does stubbing the loader’s fetch call before render produce the same serialized loader data as the production implementation?
2. Can the test assert client hydration matches the mocked server output without accessing production credentials?
3. When should the mock be installed relative to Remix’s request handler to avoid execution-order differences in Remix 2.0?