Use nix for testing environment

.busted

@@ -0,0 +1,13 @@
+return {
+  _all = {
+    coverage = false,
+    lpath = "lua/?.lua;lua/?/init.lua",
+    lua = "nlua",
+  },
+  default = {
+    verbose = true
+  },
+  tests = {
+    verbose = true
+  },
+}

.github/workflows/ci.yaml

@@ -2,15 +2,28 @@
 name: NeoVim tests
 on: [push]
 jobs:
-  plenary-tests:
+  code-quality:
     runs-on: ubuntu-latest
     env:
       XDG_CONFIG_HOME: ${{ github.workspace }}/.config/
     steps:
       - uses: actions/checkout@v4
-      - uses: rhysd/action-setup-vim@v1
+      - uses: cachix/install-nix-action@v31
         with:
-          neovim: true
-          version: v0.11.0
-          arch: 'x86_64'
-      - run: make test
+          nix_path: nixpkgs=channel:nixos-unstable
+
+      - name: Populate Nix store
+        run:
+          nix-shell --run 'true'
+
+      - name: Type-check with lua-language-server
+        run:
+          nix-shell --run 'make lint'
+
+      - name: Check formatting with stylua
+        run:
+          nix-shell --run 'make fmt-check'
+
+      - name: Run busted tests
+        run:
+          nix-shell --run 'make test'

Makefile

@@ -1,16 +1,14 @@
-PLENARY_DIR=~/.local/share/nvim/site/pack/test/opt/plenary.nvim
-
-all: lint test
+all: lint fmt-check test
 
 lint:
 	lua-language-server --check=lua/u/ --checklevel=Error
-	lx check
+	@# lx check
+
+fmt-check:
+	stylua --check .
 
 fmt:
 	stylua .
 
-test: $(PLENARY_DIR)
-	NVIM_APPNAME=noplugstest nvim -u NORC --headless -c 'set packpath+=~/.local/share/nvim/site' -c 'packadd plenary.nvim' -c "PlenaryBustedDirectory spec/"
-
-$(PLENARY_DIR):
-	git clone https://github.com/nvim-lua/plenary.nvim/ $(PLENARY_DIR)
+test:
+	busted

shell.nix

@@ -0,0 +1,19 @@
+{
+  pkgs ?
+    import
+      # neovim@0.11.1: https://history.nix-packages.com/package/neovim/0.11.1
+      (fetchTarball "https://github.com/nixos/nixpkgs/tarball/e73c3bf29132da092f9c819b97b6e214367eb71f")
+      { },
+}:
+pkgs.mkShell {
+  packages = [
+    pkgs.git
+    pkgs.gnumake
+    pkgs.lua-language-server
+    pkgs.lua51Packages.busted
+    pkgs.lua51Packages.luarocks
+    pkgs.lua51Packages.nlua
+    pkgs.neovim
+    pkgs.stylua
+  ];
+}