Unit Test Generation

Generate unit tests covering happy path, edges, and failures with strong assertions.

Testing & ReviewBeginner

Why

GitHub's 2024 survey found 92% of US respondents use AI coding tools for test case generation, and 98% of organizations have experimented with AI for tests. Good unit tests catch regressions and document intent.

AI generates them fast, but only useful if you require edge cases and exact-value assertions instead of 'doesn't throw'.

When

Use for any non-trivial function. Skip for trivial getters/setters.

How

1. Give the function + types + an example call. 2. Ask: "list edge cases first; then a test per case with exact-value assertions". 3. Require: happy path, each edge, each failure mode. 4. Run coverage; ask for tests on uncovered branches. 5. Reject "not.toThrow" assertions — demand exact values.

Example

fn: parseAge(input: string): number | null Edges: "", "abc", "-5", "999", " 42 ", "0", "2.5" Tests: expect(parseAge("42")).toBe(42); expect(parseAge("abc")).toBeNull(); expect(parseAge("-5")).toBeNull(); // etc. Coverage 100%; no "not.toThrow" in the file.

Common Problems

⚠Error: Cannot find module 'jest' / 'vitest' → run `npm install --save-dev vitest` (or jest); verify the test script in package.json.
⚠Error: "Test timed out after 5000ms" → increase `testTimeout` in config or await the async operation; common with network calls.
⚠AssertionError: expected undefined to equal 'x' → the mock returned undefined; verify the mock setup returns the expected shape.

Best Practices

✓Enumerate edge cases before writing tests.
✓Assert exact return values, not just absence of throws.
✓Measure the outcome with a concrete metric (time saved, defect rate, test coverage) so the practice can be justified and improved.

FAQ

What is Unit Test Generation?

Generate unit tests covering happy path, edges, and failures with strong assertions. It helps developers quickly grasp the core value and use cases of Unit Test Generation.

How do I get started with Unit Test Generation?

To get started with Unit Test Generation, focus on these points first: Give the function + types + an example call.

What are common mistakes with Unit Test Generation?

Common mistakes when using Unit Test Generation include: Error: Cannot find module 'jest' / 'vitest' → run `npm install --save-dev vitest` (or jest); verify the test script in package.json.; Error: "Test timed out after 5000ms" → increase `testTimeout` in config or await the async operation; common with network calls.; AssertionError: expected undefined to equal 'x' → the mock returned undefined; verify the mock setup returns the expected shape..

What are the best practices for Unit Test Generation?

Best practices for Unit Test Generation include: Enumerate edge cases before writing tests.; Assert exact return values, not just absence of throws.; Measure the outcome with a concrete metric (time saved, defect rate, test coverage) so the practice can be justified and improved..

How do I learn more about Unit Test Generation?

Start with the official docs, then search real-world examples on GitHub. Validate patterns in a small scratch repo before applying them to production code.