Steamworks.NET and that "Spacewar" game

So the question is a little weird, but I just can't find any information about this that is clear and not 6 years old.
I've done some experiments testing p2p networking with Steamworks.NET and got a little unsure about something.
Documentation says that you are supposed to be a steamwork developer with a game already published (greenlit) to use this wrapper. But untill you do that, it just uses the default game id which is 480 (Spacewar), and actually allows you to test anything. (Steam will just show you playing Spacewar, when you are actually playing your own game).
So what exactly is Spacewar? Is it intended to be used as a test field, or is it just some broken old game? I can't even find it on Steam.
I know that this game was (or still is) abused by pirates to make it possible to play pirated games online. I also heard about it getting involved in people getting banned.

What I had in mind is building a complete game prototype, that would "pretend" to be spacewar on steam, so if I wanted to test it with people, we wouldn't have to worry about NAT. (And if/when the game is released and published, there would be no need to integrate anything).
So would that be ok, or could it get people banned?

 

I am interested in this also.

 

It is quite likely a reference to the historic early video game "Spacewar!".

 

spacewar is a test multiplayer project that i think you can get the source code to if you're a steamworks dev. i vaguely remember stumbling across it in their docs.

no idea what valve would do if anything for using its app id during development.