code: def test_str_defaults_to_policy_max_line_length(self):
      m = self._str_msg("Subject: long line" + " ab" * 50 + "\n\n")
      self.assertEqual(len(str(m).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 6 for calling the TestEmailMessage obj's underlying member method code with example usage: obj.test_str_defaults_to_policy_max_line_length() without return types