Question

118

How to test event emitters in node

rated 0 times [ 120] [ 2] / answers: 1 / hits: 28822 / 10 Years ago, sun, november 30, 2014, 12:00:00

Lets say I want to write this simple task. But I want to write a test validating that:

This task emits object.

Object has a property name.

I'm testing with mocha and chai expect.

Thanks in advance. I've tried every possible variant that came to mind, but could not come up with a solution.

var util = require('util'),

    EventEmitter = require('events').EventEmitter;



function SomeTask() {

  var self = this;



  setInterval(function() {

    self.emit('data', { name: 'name' });

  }, 5000);

}



util.inherits(SomeTask, EventEmitter);



module.exports = SomeTask;

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devlin

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answered 10 Years ago leannjaidynd · Accepted Answer

Here's an example using spies. https://github.com/mochajs/mocha/wiki/Spies

var sinon = require('sinon');

var EventEmitter = require('events').EventEmitter;



describe('EventEmitter', function(){

  describe('#emit()', function(){

    it('should invoke the callback', function(){

      var spy = sinon.spy();

      var emitter = new EventEmitter;



      emitter.on('foo', spy);

      emitter.emit('foo');

      spy.called.should.equal.true;

    })



    it('should pass arguments to the callbacks', function(){

      var spy = sinon.spy();

      var emitter = new EventEmitter;



      emitter.on('foo', spy);

      emitter.emit('foo', 'bar', 'baz');

      sinon.assert.calledOnce(spy);

      sinon.assert.calledWith(spy, 'bar', 'baz');

    })

  })

})