code: def find_config(test_file=None, defaults=None, root=os.curdir):
      
      if defaults is None:
          defaults = [".benchbuild.yml", ".benchbuild.yaml"]
  
      def walk_rec(cur_path, root):
          cur_path = local.path(root) / test_file
          if cur_path.exists():
              return cur_path
  
          new_root = local.path(root) / os.pardir
          return walk_rec(cur_path, new_root) if new_root != root else None
  
      if test_file is not None:
          return walk_rec(test_file, root)
  
      for test_file in defaults:
          ret = walk_rec(test_file, root)
          if ret is not None:
              return ret
docs: Find the path to the default config file.
  
      We look at :root: for the :default: config file. If we can't find it
      there we start looking at the parent directory recursively until we
      find a file named :default: and return the absolute path to it.
      If we can't find anything, we return None.
  
      Args:
          default: The name of the config file we look for.
          root: The directory to start looking for.
  
      Returns:
          Path to the default config file, None if we can't find anything.