chore: plenary tests POC: add make entry, specify tests

tests/unit/utils_spec.lua

@@ -5,9 +5,6 @@ local stub = require("luassert.stub")
 local utils = require("nvim-tree.utils")
 
 describe("utils.path_add_trailing", function()
-  before_each(function()
-  end)
-
   it("trailing added", function()
     assert.equals("foo/", utils.path_add_trailing("foo"))
   end)
@@ -22,9 +19,6 @@ describe("utils.canonical_path", function()
     stub(vim.fn, "has")
   end)
 
-  after_each(function()
-  end)
-
   it("is windows", function()
     vim.fn.has.on_call_with("win32unix").returns(1)
     assert.equals("C:\\foo\\bar", utils.canonical_path("c:\\foo\\bar"), "should be uppercase drive")