code: def cluster_spec(self):
      return None
  
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 1 for calling the MockBaseClusterResolver obj's underlying member method code with example usage: obj.cluster_spec() and returns: None