<!--
  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

{
                  type: 'span',
                  nodeType: 'host',
                  props: {className: 'Foo2'},
                  instance: null,
                  rendered: ['Literal'],
                },
                {
                  type: Qoo,
                  nodeType: 'component',
                  props: {},
                  instance: null,
                  rendered: {
                    type: 'span',
                    nodeType: 'host',
                    props: {className: 'Qoo'},
                    instance: null,
                    rendered: ['Hello World!'],
                  },
                },
              ],
            },
          },
        },
      }),
    );
  });
  it('can update text nodes when rendered as root', () => {
    const renderer = ReactTestRenderer.create(['Hello', 'world']);
    expect(renderer.toJSON()).toEqual(['Hello', 'world']);