code: def internal_ip(self, node_id):
      if self.fail_to_fetch_ip:
          raise Exception("Failed to fetch ip on purpose.")
      if node_id is None:
          # Circumvent test-cases where there's no head node.
          return "mock"
      with self.lock:
          return self.mock_nodes[node_id].internal_ip
  
imports: import re
  import threading
  from subprocess import CalledProcessError
  from typing import Callable, Dict, List, Optional
  from ray.autoscaler.node_provider import NodeProvider
label_desc: Use image node_id 7 for calling the MockProvider obj's underlying member method code with example usage: obj.internal_ip(node_id) and returns: str, self