Step - Implement and Test Subsystems
Classic techniques, such as stepwise refinement, are used to
implement each of the subsystems.
Subsystems are validated in isolation.
Informal proofs of correctness for the subsystem are developed.
Identify necessary conditions for correct functioning.
Try to minimize conditions, and test input values whenever possible.
Software testing is used as a confidence building measure.
Intro OOP, Chapter 3, Slide 38