Phase 3 — Tests as Specification

Chapters 38, 39, 40, 41: Verify

Your role: Verifier — "I can define correct and prove it"

A type signature tells AI what shape the code should have. A test tells AI what it should do. Phase 3 teaches control flow (how code makes decisions and repeats), pytest (how you define "correct" before implementation exists), iterating on AI output (the feedback loop that makes TDG reliable), and error handling (anticipating what can go wrong). By the end, you write complete test suites that serve as the full specification AI implements against.

#	Chapter	Key Focus
38	Control Flow — Through the Lens of Testing	How code makes decisions and repeats
39	pytest Deep Dive	Defining "correct" before implementation
40	Iterating on AI Output — The Feedback Loop	The cycle that makes TDG reliable
41	Error Handling and Exceptions	Anticipating what can go wrong