Agile Software Development

Bugs used to be something very distracting and unpleasant for the software developers. For management they can be even worth - the effort and time bugs need to be fixed is poorly estimatable. Sometimes these number are complete question marks. This predictability drop is one of the reasons why agile methods advocate striving for bug-free development as possible

Scrum teams don't like bugs just as any other teams. There are multiple approaches to handle bugs from entering into the product backlog and making them wait until the end of the sprint to allocating some "maintenance slots" in the sprint to a more-or-less expected amount of maintenance. The sad truth is in that amount of bugs discovered and amount of time needed to fix them is often not predictable even roughly. Especially for teams that are not yet used to deliver the tested features.

"To me legacy code is simply code without tests."
Michael C. Feathers “Working effectively with legacy code”

The legacy code is a known software developers’ headache. The legacy code is the difficult to change code that the developers don’t really understand. This code often is inherited from the old developers who left the company, it usually has little to no documentation and little to no testing code. Legacy code can slow down the development speed up to the real competitive problems. When it takes eternity to make a required change, a company can hardly stand a competitor that is able to release life-critical software every month.