vue/test/unit/features/options/render.spec.js

import Vue from 'vue'

describe('Options render', () => {
  it('basic usage', () => {
    const vm = new Vue({
      render (h) {
        const children = []
        for (let i = 0; i < this.items.length; i++) {
          children.push(h('li', { staticClass: 'task' }, [this.items[i].name]))
        }
        return h('ul', { staticClass: 'tasks' }, children)
      },
      data: {
        items: [{ id: 1, name: 'task1' }, { id: 2, name: 'task2' }]
      }
    }).$mount()
    expect(vm.$el.tagName).toBe('UL')
    for (let i = 0; i < vm.$el.children.length; i++) {
      const li = vm.$el.children[i]
      expect(li.tagName).toBe('LI')
      expect(li.textContent).toBe(vm.items[i].name)
    }
  })

  it('allow null data', () => {
    const vm = new Vue({
      render (h) {
        return h('div', null, 'hello' /* string as children*/)
      }
    }).$mount()
    expect(vm.$el.tagName).toBe('DIV')
    expect(vm.$el.textContent).toBe('hello')
  })

  it('should warn non `render` option and non `template` option', () => {
    new Vue().$mount()
    expect('Failed to mount component: template or render function not defined.').toHaveBeenWarned()
  })
})