The testing that goes into certifying the engines that power these aircraft—the engineering marvels that can send a 600,000-pound Boeing 777 over 500 mph—are no less extreme. The engines are designed to suck in air, but they have to be capable of taking on everything else they may encounter in the sky, most notably birds and bad weather. To ensure that's the case, manufacturers run tests that are as straightforward as they are awesome: They turn on the jets and start throwing things in there.
There is a very interesting article that was published on wired.com back in November regarding jet engine testing. It is complete with awesome gifs of GE engines ingesting massive quantities of water and ice.
The article focuses on GE and their testing, but ironically has an awesome picture of a Pratt & Whitney engine on a test stand as the lead image.