Dependency Injection & Inversion of Control Containers are not about testing!
Oh, those techniques help, obviously. But it is not about unit testing.
For me, it is like saying that the main purpose interfaces is to enable easier testing.
DI & IoC are about decoupling, better flexibility, having a central place to go to and increasing the maintainability of out applications. Testing is important, but that is not the first and foremost reason.