When you test subdomains locally using localhost, it can be a pain since it won’t work out of the box for subdomains you haven’t added to /etc/hosts (since there is no support for wildcard subdomains). You can verify this easily enough:

~ $ ping john.localhost
ping: cannot resolve john.localhost: Unknown host

So, when you want something more flexible - there is another easy answer. You can use “lvh.me”, a domain which resolves to (for all subdomains):

~ $ ping lvh.me
PING lvh.me ( 56 data bytes

So, you’re actually set up for this right now:

~ $ ping john.lvh.me
PING john.lvh.me ( 56 data bytes

Pretty awesome! You need an internet connection to use it, so what I do normally is throw the subdomains that I know I’ll use into /etc/hosts - that way they work offline too!