Can I let food be tested for spoilage after freezer power outage?
I seriously doubt it. The expense and complexity of making sure there are NO pathogens in a random sample of food would be significant. And then that would be all you'd have; a statement that the tested sample had no pathogens, but who knows about the rest of the food.

Testing food in a manufacturing plant depends on the commonality of how the food has been treated; if no problems are found in the samples then you can presume no problems will be found in similarly-handled food. In your freezer, though, you may have different packagings done at different times, and when it warmed up, different parts certainly warmed to different temperatures. Finding out if one item is safe would have very little to do with whether the rest of the contents are safe.

There's also the liability of the tester; if they claimed they could tell you if your beef was safe, and then you got food poisoning, they'd be on the hook. I doubt they'd take the risk.