Couldn't you just add the domain to /etc/hosts and have it resolve that way. No need to buy domain if you are just testing locally. Also you wouldn't be exposing anything to outside world.
Perhaps I could, but I'm afraid to do it[0]. And I'd still need a matching certificate, and generating a one that browsers won't refuse to look at and make them trust it across multiple devices (including mobile) is it's own kind of hell.
--
[0] - I'm honestly afraid of DNS. I keep losing too much of my life to random name resolution failures, whose fixes work non-deterministically. Or at least I was until ~yesterday, when I randomly found out about https://messwithdns.net, and there I learned that nameservers are required to have a negative cache, which they use to cache failed lookups, often with absurdly high timeout values. That little bit of knowledge finally lets me make sense of those problems.
I was only commenting about DNS part, self signed certificates come with their own lot of trouble. At least I havent ever run into any cache issues with local resolvers.
I have previously used https://github.com/jsha/minica which makes it at least easy to create a root certificate and matching server cert. How to get that root cert trusted on different array of devices is another story.
You can add what you want to /etc/hosts, but you need to actually control a domain to get a real cert for it that your browser will trust. Otherwise, you need to mess about with self-signed certs, browser exceptions, etc.
If you already own a domain, it's pretty convenient.
