What's the best way to unit test an event being emitted in Nodejs?

Question

I\'m writing a bunch of mocha tests and I\'d like to test that particular events are emitted. Currently, I\'m doing this:

  it(\'should emit an some_event\', fun         


        

Answer 1

This method ensures the minimum time to wait but the maximum opportunity as set by the suite timeout and is quite clean.

  it('should emit an some_event', function(done){
    myObj.on('some_event', done);
  });

Can also use it for CPS style functions...

  it('should call back when done', function(done){
    myAsyncFunction(options, done);
  });

The idea can also be extended to check more details - such as arguments and this - by putting a wrapper arround done. For example, thanks to this answer I can do...

it('asynchronously emits finish after logging is complete', function(done){
    const EE = require('events');
    const testEmitter = new EE();

    var cb = sinon.spy(completed);

    process.nextTick(() => testEmitter.emit('finish'));

    testEmitter.on('finish', cb.bind(null));

    process.nextTick(() => testEmitter.emit('finish'));

    function completed() {

        if(cb.callCount < 2)
            return;

        expect(cb).to.have.been.calledTwice;
        expect(cb).to.have.been.calledOn(null);
        expect(cb).to.have.been.calledWithExactly();

        done()
    }

});