enable luarocks test

[teto]

Is your feature request related to a problem? Please describe.
I would like luarocks test to work out of the box, ie., let luarocks be able to run the gitsigns.nvim testsuite

   > building
   > running tests
   >
   > Error: could not detect test type -- no test suite for gitsigns.nvim?

Describe the solution you'd like
Looking at the luarocks code, one can:

• add a .busted file at the root
• add test.type = "busted" in the rockspec .

https://github.com/luarocks/luarocks/wiki/test

Describe alternatives you've considered
I am able to run the tests manually but luarocks test creates a convention that can work across packages and as a package manager, it makes my work easier. Also going through luarocks, you can specify dependencies just for tests.

Additional context
I think I hit #847 so I thought this would be a good time to enable tests in the nixpkgs gitsigns-nvim package but then hit > Error: could not detect test type -- no test suite for gitsigns.nvim?. I can perfectly work around it but having lua packages/neovim plugins support luarocks test would make that a ton easier. gitsigns being very popular, it can set a good example.

[lewis6991]

FYI I've kinda given up on Luarocks so this isn't something I'll want to work on.

[lewis6991]

Also the testsuite uses nvim -l as the lua interpreter, not sure if luarocks can support that.

[mrcjkb]

this can be used as a wrapper for nvim -l with luarocks. I plan on packaging it for luarocks sometime soon.