During a discussion, one of my colleagues told that he has some difficulties with his current project while trying to solve bugs. "When I solve one bug, something else stops working elsewhere", he said.
I started to think about how this could happen, but can't figure it out.
I have sometimes similar problems when I am too tired/sleepy to do the work correctly and to have an overall view of the part of the code I was working on. Here, the problem seems to be for a few days or weeks, and is not related to the focus of my colleague.
I can also imagine this problem arising on a very large project, very badly managed, where teammates don't have any idea of who does what, and what effect on other's work can have a change they are doing. This is not the case here neither: it's a rather small project with only one developer.
It can also be an issue with old, badly maintained and never documented codebase, where the only developers who can really imagine the consequences of a change had left the company years ago. Here, the project just started, and the developer doesn't use anyone's codebase.
So what can be the cause of such issue on a fresh, small-size codebase written by a single developer who stays focused on his work?
What may help?
Unit tests (there are none)?
Proper architecture (I'm pretty sure that the codebase has no architecture at all and was written with no preliminary thinking), requiring the whole refactoring?
Pair programming?
Something else?
