Stateless components have no public instance (return value of renderIntoDocument). If you were to wrap it in another (stateful) composite then you could use that instance. There is some relevant discussion in #4839. At this point, I think we're going to keep this behavior. I created an issue to document it: #4913

@jimfb I am having the same issue with scryRenderedDOMComponentsWithTag and I don't understand the "wrapping" approach you're suggesting.
I tried:

const StatelessComponent = () => <div>foo</div>

const Wrap = class Wrap extends React.Component {
  render () {
    return <StatelessComponent />
  }
}

but then calling

  const component = renderIntoDocument(<Wrap />)
  const div = scryRenderedDOMComponentsWithTag(component, 'div')

produce this error:

.../node_modules/react/lib/ReactTestUtils.js:102
    return typeof inst.render === 'function' && typeof inst.setState === 'function';
                      ^

TypeError: Cannot read property 'render' of null
    at Object.ReactTestUtils.isCompositeComponent (.../node_modules/react/lib/ReactTestUtils.js:102:23)
...

Did I misunderstood what "wrap it in another (stateful) composite" means?

Thanks!

@happypoulp That might just be a different issue. Can you open it separately?

Actually never mind we can use this one.