code: def test_streamwriter_strwrite(self):
      s = io.BytesIO()
      wr = codecs.getwriter("gb18030")(s)
      wr.write("abcd")
      self.assertEqual(s.getvalue(), b"abcd")
  
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 3 for calling the Test_StreamWriter obj's underlying member method code with example usage: obj.test_streamwriter_strwrite() without return types