Refactor, Refactor, Refactor.

Defining Refactoring, with references.

Here are the three core goals of good refactoring, now with source attribution:

1. Preserve External Behavior
   After refactoring, the system must work exactly the same from the user’s (or other components’) point of view, with no regressions, and all existing tests must still pass.

   1. As a minimum level of acceptance, pick one of the two:

      1. Add missing Unit Tests

      2. Add missing Behavioral Test

   2. Source:

      1. Martin Fowler et al., Refactoring: Improving the Design of Existing Code (Addison‑Wesley, 1999), Ch. 1.

2. Improve Internal Design
   Enhance the code’s quality, making it more readable, maintainable, and simple, without changing its functionality.

   1. This includes:

      1. Giving clear names,

      2. Reducing duplication,

      3. Breaking large methods or classes into focused, single‑responsibility units.

   2. Source:

      1. Martin Fowler et al., Refactoring (1999);

      2. Robert C. Martin, Clean Code (Prentice Hall, 2008).

3. Enable Easier Future Changes
   Make the codebase more modular and extensible so that adding new features or adapting to changing requirements becomes straightforward and low‑risk.

   1. Source:

      1. Fowler, Refactoring (1999);

      2. Martin, Clean Code (2008).