Dependency Injection for Procedural Programming

Question

Suppose I\'ve decided to write a large application in C, or any other procedural programming language. It has functions with call-dependencies that look like this:

Answer 1

You can do proper unit testing of B1, B2 and A without DI. Just like the leaf functions, B1 and B2 has valid inputs and outputs, and you test those, same with A. That B1 can use C11 and C12 internally to help you fulfill its unit tests doesn't mean they have to be injected in cases where you don't need that flexibility.