Testing flux stores with mocha, chai and sinon

I'm trying to test Flux stores with Mocha, Chai and Sinon. I've been searching for examples but couldn't find enough information to make my tests work.

I've tried many things but I'm quite blocked. This is what I have now.

Source

MyStore.js

var AppDispatcher = require('../dispatcher/AppDispatcher');
var EventEmitter = require('events').EventEmitter;
var MyStoreConstants = require('../constants/MyConstants');
var assign = require('object-assign');

var CHANGE_EVENT = 'change';

var _results = [];

function setResults(values) {
    _results = values;
}

var MyStore = assign({}, EventEmitter.prototype, {
    getResults: function () {
        return _results;
    },
    emitChange: function () {
        this.emit(CHANGE_EVENT);
    },
    addChangeListener: function (callback) {
        this.on(CHANGE_EVENT, callback);
    },
    removeChangeListener: function (callback) {
        this.removeListener(CHANGE_EVENT, callback);
    }
});

AppDispatcher.register(function (action) {
    switch (action.actionType) {
        case MyConstants.SET_RESULTS:
            setResults(action.values);
            MyStore.emitChange();
            break;
        default:
            console.log('unknown action');
     }
});

module.exports = MyStore;

MyActions.js

var AppDispatcher = require('../dispatcher/AppDispatcher');
var MyConstants = require('../constants/MyConstants');

var MyActions = {
    setResults: function (values) {
        AppDispatcher.dispatch({
            actionType: MyConstants.SET_RESULTS,
            values:values
        })
    }
};

module.exports = MyActions;

Dispatcher.js

var Dispatcher = require('flux').Dispatcher;

module.exports = new Dispatcher();

MyStoreTest.js

import {
       sinon,
       assert,
       expect
} from '../test_helper';

describe('MyStore', function() {

    var MyStore, AppDispatcher, registerSpy, MyConstants, callback;

beforeEach(() => {
    MyConstants = require('../../../src/js/constants/MyConstants.js');
    MyStore = require("../../../src/js/stores/MyStore.js");
    AppDispatcher = require("../../../src/js/dispatcher/AppDispatcher.js");
    registerSpy = sinon.spy(AppDispatcher, "register");
    AppDispatcher.register(MyStore);
    callback = registerSpy.lastCall.args[0];
});

afterEach(function () {
    registerSpy.restore();
});

it('registers a callback with the dispatcher', function() {
    expect(registerSpy.callCount).to.equal(1);
});

it('initialize with empty results', function() {
   expect(MyStore.getResults().length).to.equal(0);
});

it('fill with some results after action called', function() {
    var someResults = [3, 5, 6, 4];

    var actionSetResults = {
        actionType: MyConstants.SET_RESULTS,
        values: someResults
    };

/* I would like to fire the action and check that after the action 
is called, the value in the store changes. 
I've tried different things but none of them are working. 
probably  something about requiring something or mocking/ not mocking
something important */

   ---> send the action actionSetResults to the store

    var results = MyStore.getResults();
});

Any hint or help? Thanks!