React test-utils scryRenderedDOMComponentsWith* not traversing nested components

Question

Having an issue with testing components. I have a Voting component that renders a Vote component, and the Vote component renders two <button> tags. Using mocha+chai and react-dom/test-utils library, rendering to jsdom, I want to test that to two buttons are rendered. When I call scryRenderedDOMComponentsWithTag(component, 'button'), passing in the child Vote component, it returns a collection with the two buttons, but if I pass the parent (see below), it returns empty. I've played around with the other scryRenderedDOMComponentsWith* methods and same result. A visual check in the browser shows that the buttons are definitely rendering. Do the scryRenderedDOMComponentsWith* functions not traverse down into children of the componentTree arg? Or am I doing something wrong?

Voting.js

import React  from 'react'
import Vote   from './Vote'

const Voting = (props) => (
    <div>
      {
        <Vote {...props} />
      }
    </div>
)

export default Voting

Vote.js

import React from 'react'

class Vote extends React.Component {

  render() {
    return(
      <div className="voting">
        { this.props.pair.map(entry =>
          <button
            key={ entry }
          >
            <h1>{ entry }</h1>
          </button>
        )}
      </div>
    )
  }
}

export default Vote

Voting.spec.js

import React                  from 'react'
import ReactDOM               from 'react-dom'
import {
  renderIntoDocument,
  scryRenderedDOMComponentsWithTag,
  Simulate
}                             from 'react-dom/test-utils'

import { expect }             from 'chai'

import Voting                 from './Voting'

describe('Voting', () => {
  it('renders a pair of buttons', () => {
    const component = renderIntoDocument(
      <Voting pair={["Trainspotting", "28 Days Later"]} />
    )

    const buttons = scryRenderedDOMComponentsWithTag(component, 'button')

    expect(buttons.length).to.equal(2)
  })
})

Test output

1) Voting
   renders a pair of buttons:

  AssertionError: expected 0 to equal 2
  + expected - actual

  -0
  +2

FYI this is based on the Full Stack Redux tutorial (http://teropa.info/blog/2015/09/10/full-stack-redux-tutorial.html), I've been following along making changes as necessary to use current APIs, patterns and libraries. I've removed logic to simplify the code here. In the tutorial examples, the parent Voting component is rendered into jsdom via renderIntoDocument. scryRenderedDOMComponentsWithTag is given the parent Voting component as its componentTree arg in the example test, and finds the buttons rendered by the child Vote component - so I am expecting that it should traverse into nested components when scrying.