code: def test_writer(self):
      writer = csv_py3.DictWriter(self.output, ["a", "b", "c"])
      writer.writeheader()
      writer.writerow({"a": "1", "b": "2", "c": "☃"})
  
      result = self.output.getvalue()
  
      self.assertEqual(result, "a,b,c\n1,2,☃\n")
  
imports: import csv
  import os
  import platform
  import sys
  import unittest
  from io import StringIO
  from agate import csv_py3
  from agate.exceptions import FieldSizeLimitError
label_desc: Use image node_id 3 for calling the TestDictWriter obj's underlying member method code with example usage: obj.test_writer() without return types