Simulating a trade can happen at more than one place in the pipeline. So here we're talking about a CQG demo account where the broker maintains the account and determines if you'd have been filled or not. However, it's also possible for you to simulate the trades on your local machine with various platforms. So for instance, if you're getting full market data you'd be able to demo trade with Ninjatrader's account simulator. That is assuming you get the data for that product. Many demo accounts won't provide market data for all instruments.

You'd probably be better off trading ZB anyways...