code: def returns_true_or_raises(f):
      
      @functools.wraps(f)
      def wrapped(*args, **kwargs):
          ret = f(*args, **kwargs)
          if ret is not True:
              raise RuntimeError("Unexpected return value %r" % ret)
          return True
      return wrapped
docs: A safety net.
  
      Decorator for functions that are only allowed to return True or raise
      an exception.
  
      Args:
          f: A function whose only expected return value is True.
  
      Returns:
          A wrapped functions whose guaranteed only return value is True.