如何在Cycle.js中使用mockDOMSource测试动作流？

import { mockDOMSource, makeDOMDriver } from '@cycle/dom';
import { run } from '@cycle/run';
import { expect } from 'chai';

function main(sources) {
  const increment$ = sources.DOM.select('.increment').events('click');
  const decrement$ = sources.DOM.select('.decrement').events('click');

  const count$ = increment$.mapTo(1).merge(decrement$.mapTo(-1))
    .startWith(0)
    .scan((count, change) => count + change);

  return {
    DOM: count$.map(count =>
      div([
        button('.increment', 'Increment'),
        button('.decrement', 'Decrement'),
        p('Count: ' + count)
      ])
    )
  };
}

describe('Counter App', () => {
  it('should increment and decrement count', (done) => {
    const mockDOMSource = makeMockDOMSource({
      '.increment': {
        'click': Rx.Observable.of({})
      },
      '.decrement': {
        'click': Rx.Observable.of({})
      }
    });

    const sinks = main({ DOM: mockDOMSource });

    sinks.DOM.take(1).subscribe(vtree => {
      expect(vtree).to.deep.equal(
        div([
          button('.increment', 'Increment'),
          button('.decrement', 'Decrement'),
          p('Count: 1')
        ])
      );
      done();
    });
  });
});