code: def test_set_content_does_not_duplicate_MIME_Version(self):
      m = self._str_msg("")
      cm = self._MIME_Version_adding_CM()
      self.assertNotIn("MIME-Version", m)
      m.set_content(content_manager=cm)
      self.assertEqual(m["MIME-Version"], "1.0")
  
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 2 for calling the TestEmailMessage obj's underlying member method code with example usage: obj.test_set_content_does_not_duplicate_MIME_Version() without return types