How would you maintain legacy applications [closed]

Question

How would you maintain the legacy applications that:

1. Has no unit tests have big methods

2. with a lot of duplicated logic have

3. have No separation of concern
4. have a lot of quick hacks and hard coded strings
5. have Outdated and wrong documentation
6. Requirements are not properly documented! This has actually resulted in disputes between the testers, developers and the clients in the past. Of course there are some non-functional requirements such as shouldn't be slow, don't clash and other business logics that are known to the application users. But beyond the most common-sense scenario and the most common-sense business workflow, there is little guidance on what should be ( or not) done.

???

Answer 1

You need the book Working Effectively with Legacy Code by Michael C. Feathers.

Answer 2

Write tests as soon as you can. Preferably against the requirements (if they exist). Start with functional tests. Refactor in small chunks. Anytime you touch code, leave it cleaner and better than when you started.