Where 'it' is dependency injection, or, hey, anything else.
How about we have an interesting conversation instead of rethrashing a stupid one (here is my straw man: 'you use DI for everything without thinking.' Watch as a bash it...)?
Why do dynamic languages like python, ruby and javascript typically not use dependency injection?
You could argue that some of them (python) don't have a great unit testing background, but modern projects like node do, and you still don't see the DI pattern thrown around a lot.
In fact, you tend to only see it in languages that implement a native interface-based polymorphism, like java, c++ and c#. Even folks using go (http://openmymind.net/Dependency-Injection-In-Go/). Maybe rust too, but since the single ownership makes singletons an anti-pattern in rust, maybe not (at least I haven't seen it).
Could it be you can get by just fine for all your testing needs without DI?