code: def testHeadRequest_doesNotWrite(self):
      builder = wtest.EnvironBuilder(method="HEAD")
      env = builder.get_environ()
      request = wrappers.Request(env)
      r = http_util.Respond(request, "<b>hello world</b>", "text/html")
      self.assertEqual(r.status_code, 200)
      self.assertEqual(r.response, [])
      self.assertEqual(r.headers.get("Content-Length"), "18")
  
imports: import gzip
  import io
  import struct
  from unittest import mock
  from werkzeug import test
  from werkzeug import wrappers
  from tensorboard import test
  from tensorboard.backend import http_util
label_desc: Use image node_id 2 for calling the RespondTest obj's underlying member method code with example usage: obj.testHeadRequest_doesNotWrite() without return types