@DisplayName("starts server")
@Test
void start() {

  InetSocketAddress address = InetSocketAddress.createUnresolved("localhost", 0);
  WebsocketServerTransport serverTransport = WebsocketServerTransport.create(address);
  serverTransport
      .start(duplexConnection -> Mono.empty())
      .as(StepVerifier::create)
      .expectNextCount(1)
      .verifyComplete();
}