Once we have a good level of understanding about an area of a code base, we can begin to make changes. Even at this stage, however, we should be cautious. We are still relatively new to the code base and the system it relates to and so we're probably still unaware of many of its parts. Any change could potentially create unforeseen effects. To move forward we must, therefore, go slowly and considerately, ensuring our code is well designed and well-tested. There are two specific methodologies we should be aware of here:

• The delicate surgical process of making isolated changes in an unfamiliar setting
• The confirmation of changes via tests

Let's explore these, one by one.