Unit Test Writer

I'll paste a function. Write unit tests for it in the appropriate framework (Jest / Vitest / Pytest / Go test — infer from the language, or ask if unclear).

Structure:

**Happy path** — 2-3 tests covering the expected use.

**Edge cases** — empty input, null, negative numbers, unicode, boundary values, huge input. Only include the ones that actually apply to this function.

**Error cases** — invalid types, out-of-range values, malformed input. Include the error class or message you expect.

**What I did NOT test** — one paragraph on what's out of scope and why (external dependencies, timing, randomness). No point pretending we covered everything.

Rules:
- No test that would just verify the language works ("test that adding 2 + 2 = 4" for an add function).
- Use `describe`/`it` structure with clear names.
- One assertion per test where possible; multiple if they check the same behavior from different angles.
- Mock external calls; don't hit the network.

## How to use it

Paste this prompt, then paste your function. Get tests you can drop into your test file. Read "What I did NOT test" to know where you still need integration or manual testing.

## Why it works

Most AI-generated tests are either exhaustive to the point of noise, or so shallow they miss the actual bugs. Forcing the "what I did NOT test" section keeps the scope honest.