Working effectively with legacy code

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Unit tests run fast. If they don't run fast, they aren't unit tests.

A test is not a unit test if:
- It  talks to a database
- It communicates across a network
- It touches the file system
- You have to do special things to your environment to run it (such as editing config files)

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Dependency is one of the most critical problems in software development. Much legacy code involves breaking dependencies so that change can be easier.

The legacy code dilemma: When we change code, we should have tests in place. To put tests in place, we often have to change code.

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When you have to make a change in a legacy code base, there is an algorithm you can use.
1. Identify change points
2. Find test points
3. Break dependencies
4. Write tests
5. Make changes and refactor