code: def test_plain_text_file(self):
      path = os.path.join(resource_path, "csv/plain")
      self.sc.write(self.df, CryptoMode.PLAIN_TEXT).mode(
          "overwrite"
      ).option("header", True).csv(path)
  
      rdd = self.sc.textfile(path)
      rdd_content = "\n".join([line for line in rdd.collect()])
  
      self.assertEqual(
          rdd_content, "language,user\n" + 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 9 for calling the TestPPMLContext obj's underlying member method code with example usage: obj.test_plain_text_file() without return types