code: def message_as_clear_content(
      self, body_parts, attachments, parts, msg
  ):
      m = self._str_msg(msg)
      expected_headers = [
          h for h in m.keys() if not h.lower().startswith("content-")
      ]
      m.clear_content()
      self.assertEqual(list(m.keys()), expected_headers)
      self.assertIsNone(m.get_payload())
      self.assertEqual(list(m.iter_parts()), [])
  
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 17 for calling the TestEmailMessageBase obj's underlying member method code with example usage: obj.message_as_clear_content(body_parts, attachments, parts, msg) without return types