How to test handler with jest?

Question

I'm trying to mock an event handler from the arcgis js library using jest, but am having trouble getting a reference to the handler and triggering the callback function. I decided to mock the event handler using node's built-in events module but when I emit the event, the callback is never entered.

foo.ts

  createSomething(
    onComplete: fooCompleteCallback
  ): void {
    if (this.isReady()) {
      const handler = foo.addEventHandler((event) => {
        if (event.state === EVENT_COMPLETE) {
          handler.remove();
          onComplete(event.graphic);
        }
      });
      foo.create();
    }
  }

foo.test.ts

import events from 'events';

class foo {
  eventEmitter = new events.EventEmitter();
  
  addEventHandler = () => this.eventEmitter.on('complete', (callback) => callback({state: 'complete'}));
  isReady = jest.fn().mockImplementation(() => true);
  create = () => this.eventEmitter.emit('complete');
}
export default new foo();

Answer 1

I was pretty close, here is what the correct test code looks like

foo.test.ts

class foo {

    eventEmitter = new events.EventEmitter();
    handler = { remove: jest.fn() }

    fooEvent = {
        state: 'complete'
    }

    addEventHandler = (callback) => {
        this.eventEmitter.on('complete', () => callback(this.sketchEvent));
        return this.handler;
    };

    create = (createOptions) => { this.eventEmitter.emit('complete') };
}
export default new foo();