Just a short update on the state of Elm tooling with nix.
For a few days already all tools from the https://github.com/turboMaCk/nix-elm-tools are available within official nixpkgs, currently on the unstable channel. if you follow unstable you should be able to get for instance elm-test
using:
$ nix-channel --update
# nixos-unstable channel
$ nix-env -ia nixos.elmPackages.elm-test
# nixpkgs-unstable channel
$ nix-env -ia nixpkgs.elmPackages.elm-test