<!--
  Note: if the issue is about documentation or the website, please file it at:
  https://github.com/reactjs/reactjs.org/issues/new
-->

**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

type: Foo,
                nodeType: 'component',
                props: {},
                instance: null,
                rendered: {
                  type: 'div',
                  nodeType: 'host',
                  props: {},
                  instance: null,
                  rendered: ['Three'],
                },
              },
            ],
          },
          {
            type: 'div',
            nodeType: 'host',
            props: {},
            instance: null,
            rendered: ['Four'],
          },
        ],
      }),
    );
  });
  it('root instance and createNodeMock ref return the same value', () => {
    const createNodeMock = ref => ({node: ref});
    let refInst = null;
    const renderer = ReactTestRenderer.create(
      <div ref={ref => (refInst = ref)} />,