code: def test_sequential_serialization(
      spark_context, classification_model
  ):
      classification_model.compile(
          optimizer="sgd",
          loss="categorical_crossentropy",
          metrics=["acc"],
      )
      spark_model = SparkModel(
          classification_model, frequency="epoch", mode="synchronous"
      )
      spark_model.save("elephas_sequential.h5")
  
imports: import pytest
  from tensorflow.keras.models import Model
  from tensorflow.keras.layers import Dense, Input
  from elephas.spark_model import SparkModel
label_desc: Use image node_id 1 for calling a global function with example usage: test_sequential_serialization(spark_context, classification_model) without return types