Testing custom events react-native

Question

I am using Jest and Enzyme for my tests. I have no problem testing normal events but I am struggling to find the correct approach for how to trigger and test events within components that come from Native Modules. In my Jest setup I have the following:

jest.mock('NativeEventEmitter', () => class MockNativeEventEmitter{
  addListener = () => jest.fn()
  removeListener = () => jest.fn()
  removeAllListeners = () => jest.fn()
});

However, I am not sure within the test how I go about actually dispatching an event. So, for example I have a Native module for when the user shakes the device. Within the component itself this is setup like so:

shakeEvents: ['shaken],
deviceShakeEmitter: {},

componentDidMount() {
  this.deviceShakeEmitter = new NativeEventEmitter(Shake)
  this.deviceShakeEmitter.addListener('shaken', this['shaken'])
 },

I know for inbuilt events i can use jest.simulate('press') etc, but for the custom event I am struggling to understand how I approach this within the tests.

Answer 1

I wanted to do this as well, and I managed to find the solution in the react-native Github repo. They use the normal JS EventEmitter to mock NativeEventEmitter:

const EventEmitter = require('EventEmitter');
const RCTDeviceEventEmitter = require('RCTDeviceEventEmitter');

/**
 * Mock the NativeEventEmitter as a normal JS EventEmitter.
 */
class NativeEventEmitter extends EventEmitter {
  constructor() {
    super(RCTDeviceEventEmitter.sharedSubscriber);
  }
}

Now you just need to setup the mock, and instantiate this emitter to send out any event you like:

jest.mock('NativeEventEmitter');

const nativeEmitter = new NativeEventEmitter();
nativeEmitter.emit('SomeEventYouListenTo');