code: def test_structure(self):
      result = grpc_util.version_metadata()
      self.assertIsInstance(result, tuple)
      for kv in result:
          self.assertIsInstance(kv, tuple)
          self.assertLen(kv, 2)
          (k, v) = kv
          self.assertIsInstance(k, str)
          self.assertIsInstance(v, str)
  
imports: import contextlib
  import hashlib
  import threading
  import time
  from concurrent import futures
  import grpc
  from tensorboard.util import grpc_util
  from tensorboard.util import grpc_util_test_pb2
  from tensorboard.util import grpc_util_test_pb2_grpc
  from tensorboard.util import test_util
  from tensorboard import test
  from tensorboard import version
label_desc: Use image node_id 1 for calling the VersionMetadataTest obj's underlying member method code with example usage: obj.test_structure() without return types