Unit Test Generator

Writing tests is the part of coding most people skip when they're busy — which is exactly when bugs slip through. This tool takes a function you paste in and generates unit tests that cover the normal path, edge cases, and error conditions, giving you a solid starting suite in seconds instead of an hour.

How to use it

1. Paste your function into the Function / code box. Include any helper types or imports the function depends on so the tests reference the right names.
2. Choose a Test framework — such as Jest, Pytest, JUnit, or Mocha — so the output matches your project's tooling and syntax.
3. Generate, then read each test case. You'll typically get a happy-path test, boundary cases (empty input, zero, very large values), and error-handling assertions.
4. Drop the tests into your test directory, run your suite, and adjust any assertions that depend on your real implementation details.

When to use it

Reach for it when adding tests to legacy code that has none, when scaffolding a fresh module, or when you want a quick safety net before refactoring. It's also a great teaching aid — seeing how a function should be tested often reveals edge cases you hadn't considered. To understand unfamiliar code before you test it, run it through the code explainer; if your function builds queries, the SQL query builder can help you craft the fixtures you assert against.

Tips for better results

• Paste complete, runnable code. A function that references undefined variables produces tests that won't compile — include its dependencies.
• Match your framework exactly. Picking the wrong framework means rewriting syntax, so set it before generating.
• Call out the tricky inputs. If your function has known edge cases (negative numbers, nulls, timezones), mention them in a comment so the tests target them.
• Treat output as a first draft. Generated assertions are reasonable guesses; verify expected values against what your code actually returns.

Common mistakes to avoid

Don't assume generated tests are correct just because they pass — a test that asserts the wrong expected value will pass while hiding a bug, so review each assertion. Avoid pasting functions with heavy external dependencies (network calls, databases) without noting them; those usually need mocks, which you should add deliberately. Don't aim for 100% coverage as a vanity metric; a few meaningful tests on the risky logic beat dozens of trivial ones. Watch out for tests that are tightly coupled to implementation details rather than behavior — they break on every harmless refactor and slow you down instead of protecting you. Keep each test focused on a single behavior so that when one fails, the cause is obvious. Finally, never paste proprietary or secret-containing code you're not comfortable processing through an external tool, and strip out any real credentials before generating.