From Vibe Coding to Testing for Juniors
7 min readSenior engineers anchor every LLM‑assisted change with tests, you can too, by writing them first.
Vibe coding, the rocket fuel with no seat belt
LLMs can draft functions, refactor files, and solve edge‑case bugs in seconds. The temptation is to keep hitting "regenerate" until the code looks right and ship it. That improvisational style, often called vibe coding, works only when you can feel something is off. Seniors can have that feeling sooner because they have broken production code enough times to sense the danger.
How seniors keep chaos contained
Experienced engineers rarely lean on intuition alone. They keep a tight feedback loop:
- Write or update a test capturing the next behavior they want.
- Run the suite to watch one failure turn green.
- Commit before moving on.
The loop is so quick it feels invisible, but it is always there, guarding against unintentional regressions.
Why juniors feel the trap harder
Without that guardrail, juniors fix one bug and secretly re‑introduce three. The damage surfaces days later during code review or worse after deployment. Because each LLM suggestion rewrites more code than you can review line by line, the blast radius is larger than with manual edits.
Tests turn vibes into evidence, A failing test forces you to spell out the exact behavior you expect. When it turns green you have evidence not a vibe that the feature works. Future changes rerun the same evidence automatically, so yesterday’s confidence does not evaporate tomorrow.
Testing is the engineering version of seat belts. You hope you never need them, but you click them every time.
Habits you can adopt today
1. Write a failing test first
Pick the smallest slice of behavior: an input and the output you want.
When this fails you have a clear target.
2. Keep the loop under two minutes
Run the whole suite if it is quick; otherwise run the focused test with a watcher. The shorter the loop, the less likely you are to wander.
3. Automate regression checks
Add a CI workflow so every pull request executes the suite. Broken tests then block merges instead of breaking prod.
4. Let the LLM help write tests, too
Prompt the model with "write tests for the new slugify function". Review what it generates, tweak, and commit. The machine can draft the boilerplate; you supply the intent.
5. Treat working code as fragile
Before you refactor with an LLM, lock in current behavior with snapshot tests or golden file outputs. Now you can accept or reject model suggestions with confidence.
Common pitfalls and how to dodge them
| Pitfall | Prevention |
|---|---|
| "I’ll add tests later" | Set up a tests/ folder and CI on day one. |
| Long‑running suites | Mark slow integration tests separately and run them nightly. |
| Flaky AI‑generated tests | Read every assertion; delete ones you don’t understand. |
Finally slow down to speed up, LLMs are jet engines for productivity, but even jets need checklists. Tests are your pre‑flight inspection. The sooner you anchor your vibe coding with evidence, the faster you will move, because you will move forward instead of in circles.