code: def test_invalid_chars_in_base64_payload(self):
      source = textwrap.dedent(
          """\
              Subject: test
              MIME-Version: 1.0
              Content-Type: text/plain; charset="utf-8"
              Content-Transfer-Encoding: base64
  
              dm\x01k===
              """
      )
      msg = self._str_msg(source)
      with self._raise_point(errors.InvalidBase64CharactersDefect):
          payload = msg.get_payload(decode=True)
      if self.raise_expected:
          return
      self.assertEqual(payload, b"vi")
      self.assertDefectsEqual(
          self.get_defects(msg), [errors.InvalidBase64CharactersDefect]
      )
  
imports: import textwrap
  import unittest
  import contextlib
  from email import policy
  from email import errors
  from test.test_email import TestEmailBase
label_desc: Use image node_id 12 for calling the TestDefectsBase obj's underlying member method code with example usage: obj.test_invalid_chars_in_base64_payload() without return types