message: test(unit/specs/event): update test for new #off
diff: import BScroll from 'scroll/index'
  describe('BScroll - events', () => {
  - it('once then off', () => {
  - const wrapper = document.createElement('div')
  - const scroller = document.createElement('div')
  + let wrapper, scroller, scroll
  +
  + before(() => {
  + wrapper = document.createElement('div')
  + scroller = document.createElement('div')
  wrapper.appendChild(scroller)
  - const scroll = new BScroll(wrapper, {
  + scroll = new BScroll(wrapper, {
  tap: true,
  click: true,
  disableMouse: false
  })
  + })
  +
  + // TODO: use mock to detect event function
  + it('once then off', () => {
  let test = function () {
  return 'test once'
  }
  @@ -20,4 +26,26 @@ describe('BScroll - events', () => {
  expect(scroll._events['test'][0])
  .to.not.be.ok
  })
  +
  + it('remove the correct callback', () => {
  + let test1 = function() {}
  + let test2 = function() {}
  +
  + scroll.on('test2', test1)
  + scroll.on('test2', test2)
  +
  + const cbList = scroll._events['test2']
  +
  + expect(cbList.length)
  + .to.be.equal(2)
  + expect(cbList[0][0])
  + .to.be.equal(test1)
  +
  + scroll.off('test2', test1)
  +
  + expect(cbList.length)
  + .to.be.equal(1)
  + expect(cbList[0][0])
  + .to.be.equal(test2)
  + })
  })
  