The New TDD: Validating AI-Generated Code
Trusting AI to write your logic is like trusting a junior developer on espresso. It moves fast, but you better check its work. Here is why TDD is back.
We've all been there. You ask Cursor to "refactor the auth flow," and in 3 seconds, it spits out 200 lines of pristine-looking TypeScript. You gloss over it, hit save, and depl—CRASH.
It turns out the AI imported a deprecated library, or worse, hallucinated a function that doesn't exist.
In the era of Agentic IDEs, generating code is free. Verification is the new bottleneck. This reality is forcing a renaissance of an old, often-ignored practice: Test-Driven Development (TDD).
The Trust Gap
When humans write code, we build a mental model of the logic as we type. We "feel" the edge cases. When AI writes code, we skip that mental step. We are presented with a finished product without the context of how it got there.
The "Looks Good To Me" (LGTM) Trap
LLMs are optimized to produce probable text, not correct logic. They are statistically likely to write code that looks correct but fails in subtle, edge-case ways. If you aren't testing it, you are gambling.
Why TDD Works for Agents
TDD (writing the test before the code) was always a hard sell for humans because writing tests is boring. But for Agents? It's the perfect constraint.
A test file is essentially an executable specification. It tells the Agent exactly what "success" looks like in a language it understands (code).
- Ambiguity Killer: "Make the button blue" is vague.
expect(button).toHaveStyle({ backgroundColor: 'blue' })is absolute. - Regressions Logic: Agents love to rewrite entire files. A test suite ensures they didn't break feature A while building feature B.
The "Spec-First" Workflow
So, how does this look in 2026? Here is a powerful workflow for modern development:
Write the Test (The Spec)
Don't touch the implementation file yet. Create `utils.test.ts`. Describe the inputs and expected outputs. Treat this as your "requirements doc."
Prompt the Agent
Tell the Agent: "Implement `utils.ts` to pass the tests in `utils.test.ts`."
Watch it Fail (and Fix)
The Agent will run the test. It might fail. But modern agents (like Kiro) can read the failure output ("Expected 4, got 5") and self-correct. It's a loop.
Self-Healing Tests
This is where it gets wild. Tools like Kiro and Antigravity have integrated "loops."
You can literally run a command like:kiro run --test "npm test"
The Agent will edit code, run the test, read the error, edit code again, run test... until it passes. You can go get coffee. When you come back, you have a green test suite and working code.
The Shift: Writer to Verifier
Your job description is changing.
Old Job: Typing syntax, remembering semicolons, looking up API docs.
New Job: Defining constraints, designing edge-case tests, reviewing architectural decisions.
AI creates abundance. Abundance drops the value of "generating code" to near zero. The value shifts to guaranteeing correctness. Embrace the tests.
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