Growing Object-Oriented Software, Guided by Tests (Addison-Wesley Signature Series (Beck))

envisioned by their original implementors. The more loosely coupled your systems, the easier they are to reconfigure and reengineer.

We strongly believe that the only way to build software is incrementally. Build small pieces of end-to-end functionality, learning about the problem as you go. Apply this learning as you continue to flesh out the code, involve the customer at each step, and have them guide the process.