object : RequestBody() {
        override fun contentType(): MediaType? = null

        override fun writeTo(sink: BufferedSink) {
          sink.writeUtf8("abc")
          sink.flush()
          makeFailingCall()
          sink.writeUtf8("def")
          sink.flush()
        }
      }
    val call =
      client.newCall(
        Request(
          url = server.url("/"),