code: def test_external_source_with_serialized_pipe():
      @pipeline_def
      def serialized_pipe():
          return fn.external_source(name="es")
  
      pipe = serialized_pipe(batch_size=10, num_threads=3, device_id=0)
      serialized_str = pipe.serialize()
      deserialized_pipe = Pipeline(10, 4, 0)
      deserialized_pipe.deserialize_and_build(serialized_str)
      deserialized_pipe.feed_input("es", np.zeros([10, 10]))
  
imports: import nvidia.dali.fn
  from nvidia.dali import pipeline_def, Pipeline
  import numpy
  from nose_utils import raises
label_desc: Use image node_id 4 for calling a global function with example usage: test_external_source_with_serialized_pipe() and returns: fn