code-change-shape-classifier

Overview

Every change set has a shape: the mix of layers its files touch. A sprint of tax-rule refactors and a sprint of checkout-screen redesign produce the same commit count and very different verification needs.

The pyramid model names three test layers (unit, service, UI) and shows cost and execution speed increasing as you move up toward the higher-level tests (Fowler, TestPyramid, which credits Mike Cohn's 2009 book Succeeding with Agile for popularizing the model). That model describes where tests live. This skill describes where the change lives, which is the input the model needs.