How do I serve a localhost projects on a made up domain, such as mysite.test and testing.test simultaneously?

Solution 1:

That's what /etc/hosts are for. Edit it and add your domains after localhost to end up like this:

127.0.0.1 localhost.localdomain localhost testing.test mysite.test

You'll need root rights for this (sudo). Next, you can ping them, open in your browser, etc. They will "resolve" locally to a 127.0.0.1. If you open them through your browser via domain name (assuming you have a local webserver on 127.0.0.1), it will send a correct Host attribute and you can configure your local webserver for virtual hosts same way like with any real domain (you can easily find a lot of manuals for this on the Internet for any particular web server software).