How do I mock an endpoint that streams data in Node?

I have an endpoint that returns streaming data as newline-delimited json (ndjson). I'm trying to mock it in jest for a unit test. I've tried several ways to make this work but can't get it right. Here's what I have currently:

import * as fetch from 'node-fetch';
const ndjson = require('ndjson');
import getEvents from './getEvents';
import { EventResponseBody } from '../mocks/mockData'

describe('Events resolver', () => {

  let fetchMock: jest.SpyInstance;
  
  beforeAll(() => {
    fetchMock = jest.spyOn(fetch, 'default').mockImplementation(() => undefined);
  });

  afterEach(() => {
    fetchMock.mockReset();
  });

  afterAll(() => {
    fetchMock.mockRestore();
  });

  it('returns events for an id', async () => {
    const response = new fetch.Response(ndjson.stringify(EventsResponseBody), {status: 200})
    fetchMock.mockReturnValue(Promise.resolve(response));

    await getEvents(url, token, { id: '1' });
    expect(fetchMock).toHaveBeenCalledTimes(1);
  });
});

This code runs without error, but the test fails with a timeout error: thrown: "Exceeded timeout of 5000ms". ndjson.stringify() returns a Transform stream; do I need to explicitly emit data on that stream? If it helps, here's (working) code that utilizes the endpoint:

getEvents = (url, token, params) => (
  new Promise<T>(async (resolve, reject) => {
    const resp = fetch(url + params, {
      headers: {
        Accept: 'application/x-ndjson',
        Authorization: `Bearer ${token}`,
      },
    })
      .then(response => {
        const events = []
        response.body.pipe(ndjson.parse()).on('data', data =>
          events.push(data)
        ).on('end', () => {
          resolve(events)
        });
    }).catch(e => reject(e))
  });

Any help would be appreciated.

The answer is actually pretty straightforward; I should have read up on stream usage in Node. Simply create a stream (in my code this is done with ndjson.stringify()), return it in the response body, then write to it.

it('returns timeline updates for an identity', async () => {

    const eventsStream = ndjson.stringify();

    const response = new fetch.Response(eventsStream, {status: 200})
    fetchMock.mockReturnValue(Promise.resolve(response));
 
    EventsResponseData.forEach((json: String) => {
      eventsStream.write(json)
    })
    eventsStream.end()

    await getUpdates({}, { identityId: '1' }, {});
    expect(fetchMock).toHaveBeenCalledTimes(1);
  });