'Send "insert" etc. command, returning response as a dict.
Can raise ConnectionFailure or OperationFailure.
:Parameters:
- `request_id`: an int.
- `msg`: bytes, the command message.'

def write_command(self, request_id, msg):

    self.send_message(msg, 0)
    response = helpers._unpack_response(self.receive_message(1, request_id))
    assert (response['number_returned'] == 1)
    result = response['data'][0]
    helpers._check_command_response(result)
    return result
