code: def test_line_numbers(self):
      writer = csv_py3.DictWriter(
          self.output, ["a", "b", "c"], line_numbers=True
      )
      writer.writeheader()
      writer.writerow({"a": "1", "b": "2", "c": "☃"})
  
      result = self.output.getvalue()
  
      self.assertEqual(result, "line_number,a,b,c\n1,1,2,☃\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 5 for calling the TestDictWriter obj's underlying member method code with example usage: obj.test_line_numbers() without return types