code: def testMasterRetrieval(self):
      gce_cluster_resolver = GCEClusterResolver(
          project="test-project",
          zone="us-east1-d",
          instance_group="test-instance-group",
          task_id=0,
          port=8470,
          credentials=None,
          service=self.standard_mock_service_client(),
      )
      self.assertEqual(
          gce_cluster_resolver.master(), "grpc://10.123.45.67:8470"
      )
  
file_path: tensorflow-upstream/tensorflow/python/distribute/cluster_resolver/gce_cluster_resolver_test.py
imports: from tensorflow.python.distribute.cluster_resolver.cluster_resolver import UnionClusterResolver
  from tensorflow.python.distribute.cluster_resolver.gce_cluster_resolver import GCEClusterResolver
  from tensorflow.python.platform import test
  from tensorflow.python.training import server_lib
label_desc: Use image node_id 7 for calling the GCEClusterResolverTest obj's underlying member method code with example usage: obj.testMasterRetrieval() without return types