Software Engineer skill · test-generator

Test generator

What it does

Generates unit tests for a function or module in your test framework, covering the happy path, edge cases and error cases, with a short note on what each test proves. Use it when adding tests to new or legacy code.

Time saved: ~15–45 min per module (estimate)
Difficulty: Intermediate
Version: v1 · 2026-10-01

What you give it

Code under test (no secrets) — e.g. export function slugify(s: string) { return s.toLowerCase().trim().replace(/\s+/g, '-') }
Language and test framework — e.g. TypeScript + Vitest
Expected behaviour if not obvious (optional) — e.g. Should also drop punctuation

How it works

Infer behaviour from code and the description; when they disagree, write the test for the described behaviour and flag it.
Cover happy path, boundaries (empty, very long, unicode), invalid input and error handling.
One behaviour per test, descriptive names.
No network, clock or randomness without mocking.
Don't test private implementation details.

Output

A test file in the given framework, then a table: Test · What it proves · Expected to fail today? (if behaviour and code disagree).

Quality checklist

☑ Edge cases covered
☑ Disagreements flagged
☑ Deterministic tests

Human check: Run the tests and read them — a passing test that asserts the wrong thing is worse than none.

Example (fictional)

Code under test (no secrets): export function slugify(s) { return s.toLowerCase().trim().replace(/\s+/g, '-') }
Language and test framework: TypeScript + Vitest
Expected behaviour if not obvious: Should also drop punctuation

import { describe, it, expect } from "vitest";
import { slugify } from "./slugify";
describe("slugify", () => {
  it("lower-cases and hyphenates spaces", () => expect(slugify("Hello World")).toBe("hello-world"));
  it("drops punctuation", () => expect(slugify("Hi, there!")).toBe("hi-there"));
});

Test	Proves	Fails today?
drops punctuation	described behaviour	Yes — code keeps punctuation

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You are helping me with this task: Test generator.

## Instructions
1. Infer behaviour from code and the description; when they disagree, write the test for the described behaviour and flag it.
2. Cover happy path, boundaries (empty, very long, unicode), invalid input and error handling.
3. One behaviour per test, descriptive names.
4. No network, clock or randomness without mocking.
5. Don't test private implementation details.

## Output format
A test file in the given framework, then a table: **Test** · **What it proves** · **Expected to fail today?** (if behaviour and code disagree).

## Before you answer, check
- Edge cases covered
- Disagreements flagged
- Deterministic tests

If something important is missing from my inputs, say what you assumed. Never invent facts, numbers, names or quotes — mark anything you are unsure of as [to verify].

## My inputs
Code under test (no secrets):
{{code}}

Language and test framework:
{{framework}}

Expected behaviour if not obvious (optional):
{{behaviour}}