code: def testSimpleOverrideMasterWithRpcLayer(self):
      base_cluster_spec = server_lib.ClusterSpec(
          {
              "ps": ["ps0:2222", "ps1:2222"],
              "worker": [
                  "worker0:2222",
                  "worker1:2222",
                  "worker2:2222",
              ],
          }
      )
  
      simple_resolver = cluster_resolver.SimpleClusterResolver(
          base_cluster_spec
      )
      actual_master = simple_resolver.master(
          "worker", 2, rpc_layer="grpc"
      )
      self.assertEqual(actual_master, "grpc://worker2:2222")
  
imports: from tensorflow.python.client import session
  from tensorflow.python.distribute.cluster_resolver import cluster_resolver
  from tensorflow.python.eager import context
  from tensorflow.python.framework import config
  from tensorflow.python.framework import test_util
  from tensorflow.python.platform import test
  from tensorflow.python.training import server_lib
label_desc: Use image node_id 6 for calling the UnionClusterResolverTest obj's underlying member method code with example usage: obj.testSimpleOverrideMasterWithRpcLayer() without return types