This seems silly, a Hello World package benefits no one. Programmers make the conscious decision about whether they're developing a program or a library and not everything is suited to a library. Why would a game developer want to allow you to import their game as a package?
> Why would a game developer want to allow you to import their game as a package?
Well, why wouldn't they? Surely there are useful functions and procedures in there? If not, those might be outsourced into other separate ... packages.
> packages, not programs
Let me fix that for you: packages, and programs
You put all the logic in a library.
You reference the library in a very small program.
The main() functions inside those small programs are usually one or two screens worth of lines.
> Packages are a force multiplier
With NixOS, programs are packages.
I get the point about packages, but creating a separate package to host the tests for another package sounds a bit silly to me.