Dependency Injection: Turtles all the way down?

Question

So I\'m wondering about how unit testing works in regards to dealing external dependencies. Here and elsewhere I\'ve become familiar with dependency injection, and how that

Answer 1

Keep in mind the difference between unit testing and integration testing. In the former, the dependency would be mocked whereby it provides expected behavior for the purpose of testing the class which consumes the dependency. In the latter, an actual instance of the dependency is initialized to see if the whole thing works end-to-end.