Does Canva's Design API test mode reliably mirror live response schemas?

I'm building an integration against Canva's Design API and want to validate request/response handling without touching production credentials or real user designs. The API reference documents a test boolean parameter that returns a mock design object, and the developer sandbox provides OAuth credentials that operate outside live user data.

My concern is fidelity. I need my integration's parsing, error handling, and asset-rendering logic to behave identically against the mock response and a live response, but I can't confirm whether the test-mode payload preserves the full field set, data types, and nested structures of a real design object. I'm also unsure whether premium assets or brand-kit fields appear as placeholders in test mode, which could hide schema mismatches until production.

Assume the current v1 Design API and a standard registered OAuth app.

Which fields, if any, differ between the mock design returned with test: true and a live design response? Does the sandbox enforce the same rate limits as production, or should load behavior be validated separately? Is the Embed API preview a viable alternative for validating rendering without production keys?