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's