code: def _check_make_multipart(self, m, msg_headers, payload):
      count = 0
      for name, value in msg_headers:
          if not name.lower().startswith("content-"):
              self.assertEqual(m[name], value)
              count += 1
      self.assertEqual(len(m), count + 1)  # +1 for new Content-Type
      part = next(m.iter_parts())
      count = 0
      for name, value in msg_headers:
          if name.lower().startswith("content-"):
              self.assertEqual(part[name], value)
              count += 1
      self.assertEqual(len(part), count)
      self.assertEqual(part.get_payload(), payload)
  
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 10 for calling the TestEmailMessageBase obj's underlying member method code with example usage: obj._check_make_multipart(m, msg_headers, payload) without return types