Unit Test Generator

The unit test generator produces tests for both Jest and Vitest. Both use the same describe/it/expect API, so the generated tests are compatible with either framework. Jest is the most widely used JavaScript testing framework. Vitest is the modern Vite-native alternative that is faster and has better TypeScript support out of the box.

Pure functions — those with no side effects, that return the same output for the same input — produce the best generated tests. The generator handles: simple return values, error throwing, null/undefined handling, array operations, and object transformations. Functions with database calls, network requests, or global state need manual mocking setup not covered by this generator.

For Jest: install jest and @types/jest, then run npx jest. For Vitest: install vitest, add 'test' script to package.json (vitest run), then npm run test. Both support TypeScript natively with minimal config. The generated test file should be placed alongside your source file with a .test.ts or .spec.ts extension.

describe() groups related tests into a suite — typically one describe per function or module. it() and test() are identical — both define a single test case. Convention: use describe('functionName') and it('returns X when given Y') for readable test output. The generated tests follow this convention.

TDD means writing tests before implementing the function: write a failing test, implement enough code to pass it, then refactor. It produces better-designed, more testable code and catches requirements early. This generator works for both TDD (generate from a spec) and traditional testing (generate from existing code). TDD is recommended for new features; this generator is most useful for adding coverage to existing code.