message: Use dynamic port in UDP test case
diff: @@ -196,7 +196,7 @@ CAF_TEST(remote_link_udp) {
  CAF_TEST(multiple_endpoints_udp) {
  config cfg;
  - // setup server
  + // Setup server.
  CAF_MESSAGE("creating server");
  actor_system server_sys{cfg};
  auto mirror = server_sys.spawn([]() -> behavior {
  @@ -207,7 +207,9 @@ CAF_TEST(multiple_endpoints_udp) {
  }
  };
  });
  - server_sys.middleman().publish_udp(mirror, 12345);
  + auto port = server_sys.middleman().publish_udp(mirror, 0);
  + CAF_REQUIRE(port);
  + CAF_MESSAGE("server running on port " << port);
  auto client_fun = [](event_based_actor* self) -> behavior {
  return {
  [=](actor s) {
  @@ -220,29 +222,29 @@ CAF_TEST(multiple_endpoints_udp) {
  }
  };
  };
  - // setup client a
  + // Setup a client.
  CAF_MESSAGE("creating first client");
  config client_cfg;
  actor_system client_sys{client_cfg};
  auto client = client_sys.spawn(client_fun);
  - // acquire remote actor from the server
  - auto client_srv = client_sys.middleman().remote_actor_udp("localhost", 12345);
  + // Acquire remote actor from the server.
  + auto client_srv = client_sys.middleman().remote_actor_udp("localhost", *port);
  CAF_REQUIRE(client_srv);
  - // setup other clients
  + // Setup other clients.
  for (int i = 0; i < 5; ++i) {
  config other_cfg;
  actor_system other_sys{other_cfg};
  CAF_MESSAGE("creating new client");
  auto other = other_sys.spawn(client_fun);
  - // acquire remote actor from the server
  - auto other_srv = other_sys.middleman().remote_actor_udp("localhost", 12345);
  + // Acquire remote actor from the new server.
  + auto other_srv = other_sys.middleman().remote_actor_udp("localhost", *port);
  CAF_REQUIRE(other_srv);
  - // establish communication and exit
  + // Establish communication and exit.
  CAF_MESSAGE("client contacts server and exits");
  anon_send(other, *other_srv);
  other_sys.await_all_actors_done();
  }
  - // establish communication and exit
  + // Start communicate from the first actor.
  CAF_MESSAGE("first client contacts server and exits");
  anon_send(client, *client_srv);
  client_sys.await_all_actors_done();
  