jestjs/jest · error · Error

Missing method createWorker in WorkerPool

Error message

Missing method createWorker in WorkerPool

What it means

Error "Missing method createWorker in WorkerPool" thrown in jestjs/jest.

Source

Thrown at packages/jest-worker/src/base/BaseWorkerPool.ts:105

    if (this._workers[workerId].state === WorkerStates.SHUT_DOWN) {
      const {forkOptions, maxRetries, resourceLimits, setupArgs} =
        this._options;
      const workerOptions: WorkerOptions = {
        forkOptions,
        idleMemoryLimit: this._options.idleMemoryLimit,
        maxRetries,
        resourceLimits,
        setupArgs,
        workerId,
        workerPath: this._workerPath,
      };
      const worker = this.createWorker(workerOptions);
      this._workers[workerId] = worker;
    }
  }

  createWorker(_workerOptions: WorkerOptions): WorkerInterface {
    throw new Error('Missing method createWorker in WorkerPool');
  }

  async start(): Promise<void> {
    await Promise.all(
      this._workers.map(async worker => {
        await worker.waitForWorkerReady();

        await new Promise<void>((resolve, reject) => {
          worker.send(
            [CHILD_MESSAGE_CALL_SETUP],
            emptyMethod,
            error => {
              if (error) {
                reject(error);
              } else {
                resolve();
              }
            },

View on GitHub (pinned to f49721c78e)

Solutions

1. This is an internal Jest bug: a custom WorkerPool implementation must define a createWorker method. If you subclass BaseWorkerPool, implement createWorker() and return a ChildProcessWorker or NodeThreadsWorker instance.
2. If you are not extending jest-worker yourself, upgrade Jest to the latest version and report the issue to the Jest repository.

When it happens

Trigger: Thrown at packages/jest-worker/src/base/BaseWorkerPool.ts:105 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of jestjs/jest@f49721c78e (2026-08-03). Data as JSON: /data/errors/7be8508e88cf2206.json. Report an issue: GitHub.