def METHOD_NAME(symbol_name, target_module=None):
  """Reveals a symbol that was previously removed by `remove_undocumented`.
  This should be used by tensorflow internal tests only. It explicitly
  defeats the encapsulation afforded by `remove_undocumented`.
  It throws an exception when the symbol was not hidden in the first place.
  Args:
    symbol_name: a string representing the full absolute path of the symbol.
    target_module: if specified, the module in which to restore the symbol.
  """
  if symbol_name not in _HIDDEN_ATTRIBUTES:
    raise LookupError('Symbol %s is not a hidden symbol' % symbol_name)
  symbol_basename = symbol_name.split('.')[-1]
  (original_module, attr_value) = _HIDDEN_ATTRIBUTES[symbol_name]
  if not target_module: target_module = original_module
  setattr(target_module, symbol_basename, attr_value)