test: remove penlight usage

test/helpers.lua

@@ -3,7 +3,6 @@ local shared = vim
 local assert = require('luassert')
 local busted = require('busted')
 local luv = require('luv')
-local relpath = require('pl.path').relpath
 local Paths = require('test.cmakeconfig.paths')
 
 assert:set_parameter('TableFormatLevel', 100)
@@ -21,6 +20,12 @@ local module = {
   REMOVE_THIS = {},
 }
 
+local function relpath(p)
+  p = vim.fs.normalize(p)
+  local cwd = luv.cwd()
+  return p:gsub("^" .. cwd)
+end
+
 function module.isdir(path)
   if not path then
     return false