@monopalle The 2nd video above is a speed coding series and has I think 14 parts to it, you can go to the video link and in the description there is a download for the full source. The source is actually split up into 14 parts when you unzip it each part getting into more details -e,g. #1 the basics, #5 commands, 14 - the whole “game” where the server controls the players, movement and the enemies etc. I’ve not bothered watching the video as it’s too quick for me, but the code is good.
As for testing - you would test on the one machine and use the IP address of “localhost” so you run the server, and then on the same machine run the client. The first video shows a good example of this where he has the server running, and then runs the client 5 times as if it’s different players. You would create a solution in VS2015 and create 3 projects at least, 1 = client, 2 = server, 3 = shared classes - the 3rd one would contain things like “player class” etc, all this would be in one solution - you can then set the solution to run both client and server project at the same time, and just debug as normal. - Well that’s the basic understanding I have of it anyway - only been looking at it for a day or so.
I also have another link, but it’s at work and don’t have it on me, I’ll try and remember to post it tomorrow - this link is a very small console client/server - nothing to do with monogame and really shows the basics of how to use it.