code: def test_utf_8(self):
      s = io.BytesIO()
      c = codecs.getwriter("utf-8")(s)
      c.write("123")
      self.assertEqual(s.getvalue(), b"123")
      c.write("\U00012345")
      self.assertEqual(s.getvalue(), b"123\xf0\x92\x8d\x85")
      c.write("\uac00\u00ac")
      self.assertEqual(
          s.getvalue(), b"123\xf0\x92\x8d\x85" b"\xea\xb0\x80\xc2\xac"
      )
  
imports: import _multibytecodec
  import codecs
  import io
  import sys
  import textwrap
  import unittest
  from test import support
  from test.support import os_helper
  from test.support.os_helper import TESTFN
label_desc: Use image node_id 2 for calling the Test_StreamWriter obj's underlying member method code with example usage: obj.test_utf_8() without return types