private fun connect(
    peer: MockHttp2Peer,
    pushObserver: PushObserver = IGNORE,
    listener: Http2Connection.Listener = Http2Connection.Listener.REFUSE_INCOMING_STREAMS,
  ): Http2Connection {
    val connection =
      Http2Connection
        .Builder(true, TaskRunner.INSTANCE)
        .socket(peer.openSocket().asBufferedSocket(), "peer")
        .pushObserver(pushObserver)
        .listener(listener)

              override fun writeTo(sink: BufferedSink) {
                sink.write(postBytes) // push bytes into the stream's buffer
                sink.flush() // Http2Connection.writeData subject to write window
                sink.close() // Http2Connection.writeData empty frame
              }
            },
        ),
      )
    val response = call.execute()
    assertThat(response.body.string()).isEqualTo("ABCDE")