code: def is_base_dir(d):
      '''True if the dir is valid and it contains a dir called s2'''
      if not dir_param_valid(d): # pragma: no cover
          raise 
      else:
          mfn = os.path.join(d,'s2') #marker name. it must be a directory.
          return os.path.isdir(mfnf is_base_dir(d):
      '''True if the dir is valid and it contains a dir called s2'''
      if not dir_param_valid(d): # pragma: no cover
          raise 
      else:
          mfn = os.path.join(d,'s2') #marker name. it must be a directory.
          return os.path.isdir(mfn)
docs: True if the dir is valid and it contains a dir called s2