How to mock an EventEmitter on `createReadStream`?

Question

I'm trying to write a test case for when an error is emitted as a result of this code:

s3.getObject({
    Bucket: mediaBucket,
    Key: mediaId,
  }).createReadStream()

I've got a test with a dummy S3 object, and I'm using MemoryStream to cover cases where the call is successful. How do I emit an error, so I can write a test that allows me to test the behavior in .on('error') function(error)..?

Here's what I've tried, without success:

beforeEach(function () {
   var emitter = new EventEmitter;
   const s3 = {
     getObject: () => {
       return { createReadStream: () => emitter.emit('error', new Error('Random error!')) }
     },
};

Answer 1

Just emit it like you would any other event:

stream.emit('error', new Error('Random error!'));

So, the above code should look like:

const s3 = {
  getObject: () => {
    return { createReadStream: () => {
      process.nextTick(function() {
        emitter.emit('error', new Error('whoops!'));
      });
      return emitter;
    } }
  },
};