Most Web Servers Run Multiple Websites
In my situation almost every web server runs multiple sites. This is especially true for development and test sites that don't have much data. As websites get larger, that reverses to where each website might have multiple web servers and the database moves to its own server.
In most Mattifesto Devs documents, we focus on relatively small websites that single developers or small teams can build and maintain, because that's the perspective that most developers face.
Reserved IP Addresses
When setting up a private development or test web server you will create a virtual machine on VirtualBox. That machine will have the following network attributes:
a unique MAC address
a local IP address reserved for that MAC address
a public DNS A record associated with that local IP address
You will reserve IP addresses using your router. Not all routers are good at this. My cable router has bugs in this area, so I have an Apple AirPort Extreme set up in my office and all development machines are networked through that. There are many routers that are good at this, the Airport Extreme is just one of them.
We really push for this exact situation because we don't want to use a different set of skills, policies, and procedures for private servers. These skills are easy to build and will benefit you for the rest of your life.