text: const expect = chai.expect;
   import Vue from 'vue'
   import Button from '../src/button'
  
   Vue.config.productionTip = false
   Vue.config.devtools = false
  
   describe('Button', () => {
       it('存在.', () => {
           expect(Button).to.be.ok
       })
       it('可以设置icon.', () => {
           const Constructor = Vue.extend(Button)
           const vm = new Constructor({
           propsData: {
               icon: 'settings'
           }
           }).$mount()
           const useElement = vm.$el.querySelector('use')
           expect(useElement.getAttribute('xlink:href')).to.equal('#i-settings')
           vm.$destroy()
       })
       it('可以设置loading.', () => {
           const Constructor = Vue.extend(Button)
           const vm = new Constructor({
           propsData: {
               icon: 'settings',
               loading: true
           }
           }).$mount()
           const useElements = vm.$el.querySelectorAll('use')
           expect(useElements.length).to.equal(1)
           expect(useElements[0].getAttribute('xlink:href')).to.equal('#i-loading')
           vm.$destroy()
       })
       it('icon 默认的 order 是 1', () => {
           const div = document.createElement('div')
           document.body.appendChild(div)
           const Constructor = Vue.extend(Button)
           const vm = new Constructor({
           propsData: {
               icon: 'settings',
           }
           }).$mount(div)
           const icon = vm.$el.querySelector('svg')
           expect(getComputedStyle(icon).order).to.eq('1')
           vm.$el.remove()
           vm.$destroy()
       })
       it('设置 iconPosition 可以改变 order', () => {
           const div = document.createElement('div')
           document.body.appendChild(div)
           const Constructor = Vue.extend(Button)
           const vm = new Constructor({
           propsData: {
               icon: 'settings',
               iconPosition: 'right'
           }
           }).$mount(div)
           const icon = vm.$el.querySelector('svg')
           expect(getComputedStyle(icon).order).to.eq('2')
           vm.$el.remove()
           vm.$destroy()
       })
       it('点击 button 触发 click 事件', () => {
           const Constructor = Vue.extend(Button)
           const vm = new Constructor({
           propsData: {
               icon: 'settings',
           }
           }).$mount()
  
           const callback = sinon.fake();
           vm.$on('click', callback)
           vm.$el.click()
           expect(callback).to.have.been.called
  
       })
   })