code: def test_policy_on_part_made_by_make_comes_from_message(self):
      for method in ("make_related", "make_alternative", "make_mixed"):
          m = self.message(
              policy=self.policy.clone(content_manager="foo")
          )
          m["Content-Type"] = "text/plain"
          getattr(m, method)()
          self.assertEqual(
              m.get_payload(0).policy.content_manager, "foo"
          )
  
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 13 for calling the TestEmailMessageBase obj's underlying member method code with example usage: obj.test_policy_on_part_made_by_make_comes_from_message() without return types