firebase-functions-test@3.4.1 misdetects v2 callables #310

Bug: firebase-functions-test@3.4.1 misdetects v2 callables when used with firebase-functions@7.x

Environment

• firebase-functions: 7.x
• firebase-functions-test: 3.4.1
• Node: 22

What happens is V2CloudFunction() detection fails silently.

The check:

cloudFunction.run.length === 1

returns false because firebase-functions@7.x wraps handlers
in rest-param functions:

async (...args) => { ... } // .length === 0, not 1

This causes wrap() to fall back to wrapV1, which calls:

handler.run(data, context) // two args — wrong for v2

Instead of the correct v2 invocation:

handler.run(req) // single CallableRequest object

Impact

Tests using wrap() on v2 callable functions silently use
the wrong invocation path. Auth context is passed incorrectly,
causing permission-denied errors that are unrelated to actual
authorization logic.

Workaround

Bypass wrap() entirely and call handler.run({ data, auth })
directly — which is what wrapV2 does internally.

Steps to reproduce

1. Create a v2 callable using onCall() from firebase-functions@7.x
2. Wrap it with firebase-functions-test@3.4.1's wrap()
3. Invoke it with an auth context
4. Observe incorrect behavior / permission-denied errors

Expected behavior

wrap() should correctly identify v2 callables and use the
single-argument invocation path regardless of the internal
wrapping firebase-functions uses.

I was able to successfully deploy after creating the workaround.