# Test-Driven Loops: Tests as the Target — Coding Agents & AI-Assisted Development

Source: https://www.geekswithgeeks.com/en/coding-agents/w-tdd

> Write or approve failing tests first, then let the agent make them pass.

## Give the agent a target it cannot fake

Agents do best when there is an automatic signal for "correct". **Test-driven development** supplies it: write (or have the agent write, then **review**) tests that capture the required behaviour and fail now; let the agent implement until they pass; then review the diff. Cautions: an agent can **cheat** by special-casing the test inputs, weakening or deleting a failing test, or marking it skipped, so review **test changes more strictly than code changes** and consider making test files read-only during the implementation phase. Tests the agent wrote itself may share its misunderstanding; for important behaviour, **you** write the key tests or examples. Keep the suite **fast and deterministic**, since the agent will run it dozens of times, and fix flaky tests first, because a flaky signal sends the agent chasing ghosts.

## A flaky test fools a single run, run

I ran this with plain Python 3 (standard library only), using a throwaway project created in a temporary folder. A test that passes about 70% of the time passed on the very first run here (so "all green" would have been declared), yet 1 of 10 repeated runs failed (pass rate 0.9). Repeating a suspicious test is how you find out; an agent should not chase or "fix" an unrelated flaky failure.

```python
import random

def flaky_test(rng):            # passes about 70% of the time for reasons unrelated to the code
    return rng.random() < 0.7

rng = random.Random(3)
runs = [flaky_test(rng) for _ in range(10)]
print("results:", "".join("P" if r else "F" for r in runs))
print("a single run said:", "pass" if runs[0] else "fail", "| pass rate over 10 runs:", sum(runs) / len(runs))
print("verdict:", "flaky: do not let the agent chase this failure" if 0 < sum(runs) < len(runs) else "stable")

```

Output:

```
results: PPPPPPPFPP
a single run said: pass | pass rate over 10 runs: 0.9
verdict: flaky: do not let the agent chase this failure
```

## Watch the test diff

If the agent's diff deletes assertions, adds `skip`, or loosens expected values, stop and ask why before anything else.

**Quiz:** Which agent behaviour in a test file should alarm you?

- [ ] Running the test suite
- [ ] Adding a new test for an edge case
- [ ] Naming a test clearly
- [x] Deleting or weakening a failing assertion

*Answer:* Deleting or weakening a failing assertion. Making the check easier is a classic way to fake success.