Dart integration test with VM server and dartium browser - testing

Question

I'm making a library that implements both server and client parts that interacts between them via websockets:
Server use example (ran in CLI):
Server srv = await new Server("localhost:1234");
srv.onNewClientConnected.listen(print("client connected"));
Client use example (ran in browser):
Client cli = await new Cliente("localhost:1234");
cli.sendCommand(...);
(Just by creating the instances, the client should be connected and the server noticed about that connection.)
I'd like to know what would be the best way to test their interactions? Could I check both objects internals with that method?
I would like something like this:
test(".echo should receive same input from server", (){
cli.echo("message");
expect(srv.lastMessageReceived, equals("echo: message"));
expect(cli.lastResponseReceived, equals("echo: message"));
expect(srv.amountMessagesReceived, equals(1));
});

Answer 1

If I understand correctly, I'm guessing you are trying to encapsulate https://www.dartlang.org/dart-vm/dart-by-example#websockets into helpers so that you have only instances when connected. However both operations (server side binding/listening/upgrade, client side connection) is asynchronous so you will never reach the state you want by just creating the instances (or you will need an additional asynchronous methods to be notified). I would suggest creating asynchronous helpers.
Assuming you accept only one client in your server
Server server = await Server.accept("localhost:1234");
Client side:
Client client = await Client.connect("localhost:1234");
By doing so, you will have only server and client instances when connected
I like the https://pub.dartlang.org/packages/web_socket_channel package which provide a good abstraction and allow me to test my web socket client logic that will run in the browser in a simple io test.
As for testing recommendations, I personally start my web socket server in setUpAll and create my client in setUp and user a similar logic that you propose (don't forget the await though as you will need to wait for the echo response). Again the web_socket_channel package has some good testing example that you can look at (https://github.com/dart-lang/web_socket_channel/tree/master/test)