Mocha "done() called multiple times" - Fix Async Callback Bugs

By Daniel Zoghalchali·Latchkey

Mocha detected that a test’s done callback fired more than once. A callback path calls done() twice, an event handler invokes it per event, or you returned a promise while also calling done.

What this error means

A test fails with "Error: done() called multiple times." It can be intermittent - the second call may depend on timing - which makes it look flaky even though the bug is deterministic in the code.

  1) emits events
       done() called multiple times
     Error: done() called multiple times
        at Runnable.<anonymous> (node_modules/mocha/lib/runnable.js)

Common causes

done() in a handler that fires repeatedly

Calling done() inside an event listener or callback that runs more than once invokes it multiple times.

Mixing done with a returned promise

Taking done and also returning a promise can complete the test twice - once on resolution, once on the callback.

How to fix it

Call done exactly once

Use once for one-shot events, or capture the first error and return early.

it('emits ready once', (done) => {
  emitter.once('ready', () => done());   // not .on(...)
});

Pick one completion style

1. Use async/await OR done, never both in the same test.
2. In promise chains, pass done directly to .then(() => done(), done) only when you are not also returning the chain.
3. Guard error-then-success paths so only one calls done.

How to prevent it

• Prefer async/await to avoid manual done entirely.
• Use .once() for single-shot events in tests.
• Never return a promise from a test that also takes done.

Frequently asked questions

Related guides

References

• GitHub Actions documentation