I'd suggest the book [Working Effectively with Legacy Code](https://www.amazon.com/Working-Effectively-Legacy-Michael-Feathers/dp/0131177052 https://www.amazon.

I'd suggest the book [Working Effectively with Legacy Code](https://www.amazon.com/Working-Effectively-Legacy-Michael-Feathers/dp/0131177052 https://www.amazon.com/Working-Effectively-Legacy-Michael-Fe...).