If your READ permissions return a PERMISSION_DENIED, then the getDoc promise will return the error code. however since this only expects that promise.not.toBeUndefined, then the error code meets that criteria.
I fixed locally by just adding the second check to make sure that the error code != PERMISSION_DENIED
The function, expectPermissionGetSucceeds, can pass when it shouldn't.
https://github.com/firebase/quickstart-testing/blob/6ac0acf396e87e2588223151e8f0b4cf307a5e84/unit-test-security-rules-v9/test/utils.ts#L61
If your READ permissions return a PERMISSION_DENIED, then the getDoc promise will return the error code. however since this only expects that promise.not.toBeUndefined, then the error code meets that criteria.
I fixed locally by just adding the second check to make sure that the error code != PERMISSION_DENIED