I scoped my blog just to unit tests, because it's short note rather than article. DI can be useful on integration and acceptance level too - for simple apps you

I scoped my blog just to unit tests, because it's short note rather than article. DI can be useful on integration and acceptance level too - for simple apps you should be able to configure whole app or its parts as easy as you run it on production. Without DI you have to do some magic with class / module constants, which can populate on other parts.