Aspnetcore: [SignalR] Better integration with TestServer

[anurse]

Right now, it's only possible to use TestServer with the non-WebSockets transports because we only provide a way to replace the HttpMessageHandler. We should consider providing a way to provide a WebSocket "factory" so that we can integrate properly with TestServer.

It might be most appropriate here to add an alternative to WithUrl on HubConnectionBuilder. Consider this possible test code:

var server = new TestServer(webHostBuilder);
var connection = new HubConnectionBuilder()
    .WithTestServer(server, HttpTransportType.WebSockets, o => {
        // Assorted other HttpConnectionOptions
    })
    .Build();

It would be relatively simple to add this API once we have a way to swap out the WebSocket, though we'd probably need to do so in a new assembly to avoid layering issues.

[khteh]

Bear in mind that WebHostBuilder will be deprecated in future releases.

[anurse]

Yes, we're aware :). The focus is on better integration with TestServer, not necessarily using WebHostBuilder.

[Suriman]

Please, these characteristics are very important to be able to test SignalR with TestServer in integration or unit tests.