What is a verification loop for an AI coding agent?

It is a feedback cycle where the agent runs a real check (typecheck, tests, or the app) after each attempt, reads the result, and iterates until the check passes, all before reporting done. It replaces "the code looks right" with "the code proved itself", which matters because agents are optimized to produce plausible-looking output.

How do I stop an AI agent from writing code that only looks correct?

Give it a check it cannot pass by looking plausible. The cheapest is a typecheck; the strongest is a test written before the code. Put "run the tests and fix until green before reporting done" in the prompt so verification happens inside the agent's loop, not in your review.

Should I use TDD with AI coding agents?

For correctness-critical work, yes. A failing test written first is a specification the agent cannot satisfy with fluent-but-wrong code, and it closes the window where plausible bugs settle in. For trivial or exploratory changes, a lighter loop (typecheck plus existing tests) is enough.

Why does my agent make the tests pass but the behavior is still wrong?

Usually one of two reasons: the agent edited the tests to force a green result (forbid test edits in the prompt and review test diffs separately), or your tests never covered the behavior you care about (describe the wrong behavior and have the agent write a failing test for it first).

Can I let an AI agent run tests and fix failures automatically?

Yes, and it is where the speed comes from. Keep three guardrails: the tests are read-only during a fix, bound the number of retries so a stuck loop stops and asks for help, and remember that green proves the code passes your checks, not that you wrote the right checks.

CodeSmith

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One buggy task, three feedback loops. Step through and count the bugs that ship.Iteration 0/3

No feedback

The agent writes code and stops. The only check is "does it look right".

Press Step or Play to start.

Compiler only

The agent must pass a typecheck before reporting done.

Press Step or Play to start.

Full test loop

The agent must pass typecheck AND tests before reporting done.

Press Step or Play to start.

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