# The Method Use Rule

> Michael Feathers가 Working effectively with legacy code에서 제안하는 규칙:

<Michael Feathers>가 <Working effectively with legacy code>에서 제안하는 규칙:

> Before you use a method in a <legacy system>, check to see if there are [tests](https://wiki.g15e.com/pages/Unit%20test.txt) for it. If there aren't, write them. When you do this consistently, you use tests as a medium of communication. People can look at them and get a sense of what they can and cannot expect from the method. The act of making a class testable in itself tends to increase code quality. People can find out what works and how; they can change it, correct bugs, and move forward.

위 규칙을 따르면 전체 코드 중 현재 자주 쓰이는 혹은 자주 수정되는 코드 위주로 개선이 시작될 수 있다. 다른 순서에(예: 위에서 아래로, 가나다순 등) 비해 합리적이다.