One possibility is in the view file:
You can stop Magento from caching the block by adding a false parameter when you implement the block.
<?php echo $this->getChildHtml('testimonials', false) ?>
Because of
Method Summary
string getChildHtml ([string $name = ‘’], [boolean $useCache = true], [ $sorted = true])
Or you could add the cache lifetime to your testimonial class:
public function getCacheLifetime() { return null; }