What's your test network look like?

First off, I'm aware of the adage "Everyone has a test network. Some people are lucky enough to have a production network." For the purposes of this post, assume that when I say "test network", I do NOT mean your production network.

So, do you have a test network? If so, what does it look like?

• Do you have a couple of spare random switches and routers laying around you can use to test new features, while connected to your production network?
• Do you have one of each type of device, so you can test new OS versions?
• Do you have an exact mirror of your network topology?