code: def test_write_and_read_plain_parquet(self):
      parquet_path = os.path.join(
          resource_path, "parquet/plain-parquet"
      )
      # write as a parquet
      self.sc.write(self.df, CryptoMode.PLAIN_TEXT).mode(
          "overwrite"
      ).parquet(parquet_path)
  
      # read from a parquet
      df_from_parquet = self.sc.read(CryptoMode.PLAIN_TEXT).parquet(
          parquet_path
      )
  
      content = "\n".join(
          [
              str(v["language"]) + "," + str(v["user"])
              for v in df_from_parquet.orderBy("language").collect()
          ]
      )
      self.assertEqual(content, self.data_content)
  
file_path: BigDL/python/ppml/test/bigdl/ppml/test_ppml_context.py
imports: import unittest
  import os
  import random
  import shutil
  from bigdl.ppml.ppml_context import *
  from pyspark.sql.types import StructType, StructField, StringType
label_desc: Use image node_id 7 for calling the TestPPMLContext obj's underlying member method code with example usage: obj.test_write_and_read_plain_parquet() without return types