title: TypeError: Jest: a transform must export something
body: <p>After configuring <code>jest</code>, <code>node.js</code> and <code>typescript</code> the script <code>npx jest</code> throws the error in a console</p>
  <pre><code>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)
  </code></pre>
  <p>jest.config.js</p>
  <pre><code>export default {
    roots: [
      '&lt;rootDir&gt;/src'
    ],
    testMatch: [
      '**/__tests__/**/*.+(ts)',
      '**/?(*.)+(test).+(ts)'
    ],
    transform: {
      '^.+\\.(ts)$': 'ts-jest'
    }
  }
  </code></pre>
  <p>Where did I fail to configure it correctly?</p>