How can I test a Grunt integration that relies on external services without using production credentials?

I need to run a Grunt task that executes a shell command (e.g., a curl request) to verify an integration with a third‑party API. To avoid exposing real secrets, I want to supply test‑only credentials through grunt‑env and have grunt‑shell use those values in its command template. I am unsure how to isolate the environment so that the shell task does not inadvertently fall back to production variables stored elsewhere, and whether the templating mechanism will safely substitute the dummy values at runtime.

How can I configure grunt‑env to provide test‑only credentials for a shell task? How can I ensure the shell task does not accidentally read real production env vars? Is there a way to mock the external service within the grunt task?