Teaching an AI Agent to Do TDD (And Actually Mean It)

One of the more interesting problems I've been sitting with lately is this: how do you make an AI coding agent disciplined? Not capable — that part is mostly solved. But disciplined. The kind of discipline that stops a developer from writing five tests at once before any of them are green. The kind that insists every acceptance criterion has a named test before you call the story done. That's the hard part. The Problem With "Just Tell It" My first instinct was to write a rule: "follow TDD." Simple enough. But vague instructions produce vague compliance. The agent would write a test, write all the implementation, then nod along when you asked if it did TDD. Technically yes. Practically no. The fix was to get specific about the atomic unit . Not "write tests first" but "write exactly one failing test, make it pass, commit — then and only then write the next test." That single constraint changes the whole rhythm. It forces small commits, it surfaces design issues early, and crucially, it'