<!--
  Note: if the issue is about documentation or the website, please file it at:
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**Do you want to request a *feature* or report a *bug*?**

bug.

**What is the current behavior?**

```js
  renderer.create(
    <Fragment>
      <Fragment>foo</Fragment>
    </Fragment>
  )
  .toTree()
```

> Invariant Violation: toTree() does not yet know how to handle nodes with tag=10

https://codesandbox.io/s/olky92m01y

**What is the expected behavior?**

returns a tree.

**Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?**

16.2.0

log.push('unmount ' + this.props.name);
      }
    }
    const renderer = ReactTestRenderer.create(<Log key="foo" name="Foo" />);
    renderer.update(<Log key="bar" name="Bar" />);
    renderer.unmount();
    expect(log).toEqual([
      'render Foo',
      'mount Foo',
      'render Bar',
      'unmount Foo',
      'mount Bar',
      'unmount Bar',
    ]);
  });
  it('gives a ref to native components', () => {
    const log = [];
    ReactTestRenderer.create(<div ref={r => log.push(r)} />);
    expect(log).toEqual([null]);
  });
  it('warns correctly for refs on SFCs', () => {
    function Bar() {
      return <div>Hello, world</div>;
    }
    class Foo extends React.Component {
      render() {
        return <Bar ref="foo" />;
      }
    }
    class Baz extends React.Component {