Gets a string of the tasks running on `backend`. This string will 
        either be an integer if the backend is up, or else 'down'.Raises 
        ValueError if `backend` is not registered with the client.
        
        Example:
        
        >>> frontend = FrontEnd(['localhost', '****'])
        >>> frontend.get_tasks('localhost')
        '5'
        >>> frontend.get_tasks('****')
        'down'
        >>> frontend.get_tasks('unregistered')
        Traceback (most recent call last):
        [...]
        ValueError: No such backend!

def get_tasks(self, backend):
        """
        Gets a string of the tasks running on `backend`. This string will 
        either be an integer if the backend is up, or else 'down'.Raises 
        ValueError if `backend` is not registered with the client.
        
        Example:
        
        >>> frontend = FrontEnd(['localhost', '****'])
        >>> frontend.get_tasks('localhost')
        '5'
        >>> frontend.get_tasks('****')
        'down'
        >>> frontend.get_tasks('unregistered')
        Traceback (most recent call last):
        [...]
        ValueError: No such backend!
        """
        try:
            res = self.send_signal(backend, STATUS)
        except BackendNotAvailableError:
            res = 'down'
        return res