How to setup and run a test of 32 players in a network game?

I'm using the Steam API, and FacePunch networking for a PC game. 
In the past for console, I'd invite 8-12 people over and use every machine in the office.
Now, the player count is too high for that to work.

What can be done to test?

Because you have PC games, you can build simple AI bots that "know" how to play the game, even if they are not particularly great at it.

You might even write little scripts; spawn -- go to point A -- go to point B -- take out weapon -- wait until another player is seen -- aim and shoot -- put away weapon -- repeat. Or whatever makes sense for your game.

If you make it so your game doesn't need to render to run well, or if you can render to a small window (240x160 or whatever,) then you can hopefully run many copies of the game client on a single PC / laptop, as the main power suck for most games is rendering.