How to memorize and organize the memorization of a large number of dependencies?

Question

MySQL

Greetings
I ran into the problem of remembering, organizing and working with a large number of dependencies. A lot of different code, and if you change something somewhere, it can affect other code, and other code can affect other code, and so on. Keeping everything in mind is possible, but difficult. What methods, techniques, techniques, software exist, what do you use, how do you organize such work to catch the dependencies of one from the other?

Answer 1

This problem is solved through system design and development documentation.

Answer 2

> A lot of different code, and if you change something somewhere, it may affect other code
This question is closed by unit tests
> and development documentation.