clexmond/lithium — comment on commit 9dbd5165d42334e56f80f0078c9f31dbe62c9737
File: test/Unit.php line 528
By clexmond:

The closure is effectively the result here. It would contain code within it that is expected to throw an exception. This is a more flexible and more abstract way of testing for exceptions than having to include try / catch blocks throughout your test cases.