code: def get_external_ip(self, worker_index: int) -> str:
      return "1.2.3.4"
  
file_path: ray/python/ray/tests/gcp/test_gcp_tpu_command_runner.py
imports: import pytest
  import os
  from ray.tests.test_autoscaler import MockProvider, MockProcessRunner
  from ray.autoscaler._private.gcp.tpu_command_runner import TPUCommandRunner
  from ray.autoscaler._private.command_runner import SSHCommandRunner
  from ray._private import ray_constants
  from getpass import getuser
  import hashlib
  from unittest.mock import patch
label_desc: Use image node_id 3 for calling the MockTpuInstance obj's underlying member method code with example usage: obj.get_external_ip(worker_index) and returns: str