Test-Driven Development

Purpose

• Drive implementation from observable behavior.
• Reproduce bugs before fixing them.
• Keep code changes tightly coupled to expected outcomes.
• Use tests as design tools, not just safety nets.
• Reduce regressions by proving each behavior change.

Activation Signals

• Use this skill when adding a new feature with clear acceptance behavior.
• Use this skill when fixing a bug that should never recur.
• Use this skill when API shape is easier to design from usage than internals.
• Use this skill when reviewers will ask for evidence.
• Use this skill when the codebase already has a strong test culture.

Core Cycle