Hmm, maybe go offline while you test your function. That may defeat the point when using Steam, but I know Steam works really well offline.
I actually run a whole LAN party Offline with Steam so I don't need 6 Steam accounts. Some games like The Ship, Terraria, Half-Life 2 Deathmatch and Counter-Strike: Source all run well offline.
I even setup a second network connection in Mint so I can easily switch between internet and offline (10.0.0.1)
What exactly are you trying to do?