Use nix for testing environment

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