Write a regression test

[benfowler]

We need an automated test that, ideally, starts Neovim with a minimal reproduction of the environment (Telescope, LuaSnip, some snippets) and ensures that it's working as expected. It should be written to be usable in a CI/CD pipeline (like a GitHub Action).

Prior art:

See examples in other Telescope plugins listed here. Here are some other Telescope extensions that implement Lua unit tests:

cljoly/telescope-repo.nvim: Makefile-driven Lua test runner with minimum reproduction of the environment