if ($this->getTestSku()) {
...
} elseif ($this->getTestOffset() >= 0 && $this->getTestLimit() > 0) {
...
} else {
Mage::throwException(sprintf("Invalid parameters for test mode: sku %s or offset %s and limit %s", $this->getTestSku(), $this->getTestOffset(), $this->getTestLimit()));
}