code: def testHeaders(self):
      q = wrappers.Request(wtest.EnvironBuilder().get_environ())
      body = "No GET, only POST"
      r = http_util.Respond(
          q,
          body,
          "text/plain",
          code=405,
          headers=[("Allow", "POST"), ("Content-Length", "777")],
      )
      # non-conflicting headers passed through, conflicts overridden
      self.assertEqual(r.headers.get("Allow"), "POST")
      self.assertEqual(r.headers.get("Content-Length"), str(len(body)))
  
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 12 for calling the RespondTest obj's underlying member method code with example usage: obj.testHeaders() without return types