House skill. test-driven-development owns test-first process and honest behavioral intent. This skill owns TypeScript/JavaScript test mechanics and common false-green modes. Use the repository's existing runner rather than introducing another by default.

Start from the runner and environment

Inspect package scripts and test configuration before writing tests.

Know:

runner: Bun test, Vitest, Jest, Node test, or another declared tool;
environment: Bun/Node, jsdom, happy-dom, real browser, worker, etc.;
module mode and transform pipeline;
fake-timer implementation;
setup files and global hooks;
whether tests are typechecked separately.

Do not write browser API tests into a plain Node environment and then mock the entire browser surface to make them pass. Choose the environment that matches the boundary being verified.

typescript-testing

Start from the runner and environment

Async tests must own completion