Let's say that we're testing a webserver where the pages served depended on a domain that you don't own. The most common way I know to test this is to modify your `/etc/hosts` file to contain the hostname and ip address you want to map it to.
```
192.168.1.2 custom.domain
```
I've recently discovered that the command line utility `curl` has a quick and easy option to forge the hostname of a request.
```bash
curl --resolve domain:port:ipaddr url
```
There are also browser extensions that you can use such as [LiveHosts](https://github.com/Aioros/livehosts) to get around this as well. This post isn't entirely useful when talking about permanent services.
If this is going to be a publicly facing service, then you should just set the records of your domain name to point to the server.
