JavaScript/Node – Why isn’t my jest mock being called?

I am writing a unit test for a pubsub component in my service. My directory structure looks like this:

src
|
|-- common
|    |
|    |-- pubsub
|        |
|        |-- publish_to_topic.ts
|-- publishers
    |
    |-- publish_event.ts

tests
|
|-- publishers
    |
    |-- publish_event.test.ts

The file publish_to_topic.ts looks like this

export default async publishToTopic<T>(
    pubSubClient,
    topic,
    data) {
    ...
}

And is called by publish_event.ts like so:

import { pubSub } from './../common/pubsub_client';
import publishToTopic from './../common/pubsub/publish_to_topic';

export async function publishEvent(
   event,
   time,
   metadata = {}) {
  return publishToTopic(
    pubSub,
    'my-topic',
    { data: event, timestamp: time, metadata });
}

Lastly in my test file publish_event.test.ts, I set up a mock:

import { publishEvent } from './../../src/publishers/avoidance_area_change_event';

describe("test publisher", () => {
  let mockPublishToTopic;

  beforeEach(() => {
    mockPublishToTopic = jest.fn();
    jest.mock('./../../src/common/pubsub/publish_to_topic', () => mockPublishToTopic);
  });

  it("test1", async () => {
    const data = ...;
    const time = new Date();
    const metadata = {};

    publishEvent(event, time, metadata);

    expect(mockPublishToTopic).toBeCalled();
  });
})

Alas, my test fails:

Expected number of calls: >= 1
Received number of calls:    0

Can anyone explain where I’ve gone wrong? Thank you.

Answer

You have your mocked function wrapped in a second function (without calling the mock itself).

Update to this:

beforeEach(() => {
    mockPublishToTopic = jest.fn();
    jest.mock('./../../src/common/pubsub/publish_to_topic', mockPublishToTopic);
  });