$ yarn $ yarn tsc yarn run v1.22.5 $ tsc Done in 1.71s. $ yarn tsc-tr yarn run v1.22.5 $ tsc -p tsconfig.tr.json src/index.test.ts:1:1 - error TS2593: Cannot find name 'test'. Do you need to install type definitions for a test runner? Try `npm i --save-dev @types/jest` or `npm i --save-dev @types/mocha` and then add `jest` or `mocha` to the types field in your tsconfig. 1 test("42", () => { ~~~~