it('new docs emitted', function(done) {
    let observer = new MongoCursorObserver(fakeCursor, 0);
    let emit = sinon.spy(observer, 'emit');
    observer.subscribe({ next: noop });

    let doc1 = { id: 'doc1' };
    let doc2 = { id: 'doc2' };
    fakeCursor.add(doc1, 0);
    fakeCursor.add(doc2, 1);

    setTimeout(() => {
      expect(emit.calledOnce).to.equal(true);
      expect(emit.args[0][0][0].item).to.deep.equal(doc1);
      expect(emit.args[0][0][1].item).to.deep.equal(doc2);
      done();
    });
  });

 ngZone.run(() => {
   observer = new MongoCursorObserver(fakeCursor, 0);
   observer.subscribe({ next: noop });
 });