TypeError: Jest: a transform must export something

Question

After configuring jest, node.js and typescript the script npx jest throws the error in a console

TypeError: Jest: a transform must export something.
    at C:\projects\project-api\node_modules\@jest\transform\build\ScriptTransformer.js:386:19
    at processTicksAndRejections (internal/process/task_queues.js:93:5)
    at async Promise.all (index 0)
    at async ScriptTransformer.loadTransformers (C:\projects\project-api\node_modules\@jest\transform\build\ScriptTransformer.js:378:5)
    at async createScriptTransformer (C:\projects\project-api\node_modules\@jest\transform\build\ScriptTransformer.js:1105:3)
    at async C:\projects\project-api\node_modules\@jest\core\build\TestScheduler.js:283:31
    at async Promise.all (index 0)
    at async TestScheduler.scheduleTests (C:\projects\project-api\node_modules\@jest\core\build\TestScheduler.js:276:5)
    at async runJest (C:\projects\project-api\node_modules\@jest\core\build\runJest.js:387:19)
    at async _run10000 (C:\projects\project-api\node_modules\@jest\core\build\cli\index.js:408:7)

jest.config.js

export default {
  roots: [
    '<rootDir>/src'
  ],
  testMatch: [
    '**/__tests__/**/*.+(ts)',
    '**/?(*.)+(test).+(ts)'
  ],
  transform: {
    '^.+\\.(ts)$': 'ts-jest'
  }
}

Where did I fail to configure it correctly?

Answer 1

I had your same issue.

For me, it end up it was because I was having old version of following packages:

• ts-loader
• ts-jest
• ts-node