Class Parent

packages/nerv/__tests__/dom.spec.js:27–37

      const portal2 = document.createElement('div')

      class Parent extends Component {
        render () {
          return null
        }
        getChildContext () {
          return { value: this.props.value }
        }
        componentDidMount () {
          renderSubtreeIntoContainer(this, <Middle />, portal1)
        }
      }

      let m1, m2