chore: plenary tests POC

tests/unit/utils_spec.lua

@@ -0,0 +1,17 @@
+---@type Luassert
+local assert = require("luassert")
+
+local utils = require("nvim-tree.utils")
+
+describe("utils.path_add_trailing", function()
+  before_each(function()
+  end)
+
+  it("trailing added", function()
+    assert.equals(utils.path_add_trailing("foo"), "foo/")
+  end)
+
+  it("trailing already present", function()
+    assert.equals(utils.path_add_trailing("foo/"), "foo/")
+  end)
+end)