code: def test_as_string_uses_max_header_length_by_default(self):
      m = self._str_msg("Subject: long line" + " ab" * 50 + "\n\n")
      self.assertEqual(len(m.as_string().strip().splitlines()), 3)
  
imports: import unittest
  import textwrap
  from email import policy, message_from_string
  from email.message import EmailMessage, MIMEPart
  from test.test_email import TestEmailBase, parameterize
label_desc: Use image node_id 3 for calling the TestEmailMessage obj's underlying member method code with example usage: obj.test_as_string_uses_max_header_length_by_default() without return types