Practice: Design Driven Implementation
Create an implementation from the design, then write and execute unit tests against the implementation.
Perform black-box testing on new components and regression test all code prior to integrating changes.
Why adopt this practice

The Design Driven Implementation practice improves productivity by helping teams to develop a solution based on a pre-existing software design. It narrows the scope of the solution to implementation. It also facilitates the conversion between the designed solution and the actual implementation of the system as each developed module can refer to preexistent design elements. This improves productivity to achieve a better time to market. And it contributes to a better alignment between the initial business needs and the delivered system by ensuring the implementation derives from technical design and user requirements instead of ad-hoc coding.

This practice also improves the quality of the final product. Each time you develop an element, you rely on a well defined design.

Adopting this practice improves predictability and project oversight by aiding project managers to scope and plan the implementation work based on the software design elements.

Application
Additional Information
For more information on this practice,  see the practice resource page on IBM® DeveloperWorks®.