Tsd
lastmod 2026-11-10created 2022-04-142 edits
tsd is a testing tool that checks whether TypeScript type definition files (.d.ts) behave as intended. When you write test files using assertion functions such as expectType and expectError, it verifies that the declared types match the expected types and that incorrect usage produces compile errors. It is used in CI to catch declaration files drifting from the actual implementation when shipping type declarations alongside a library written in JavaScript.
Check TypeScript type definitions