Fuel\Validation\Validator::setMessage PHP Method

    public function setMessage($message)
    {
        if (!$this->lastAddedRule) {
            throw new LogicException('VAL-006: A rule should be added before setting a message.');
        }
        $this->lastAddedRule->setMessage($message);
        return $this;
    }

 /**
  * @expectedException \LogicException
  */
 public function testSetMessageException()
 {
     $this->object->setMessage('injected message');
 }