<!--
  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

render() {
        return this.props.children;
      }
    }
    const renderer = ReactTestRenderer.create(
      <div>
        <Foo>
          <div>One</div>
          <div>Two</div>
          <Foo>
            <div>Three</div>
          </Foo>
        </Foo>
        <div>Four</div>
      </div>,
    );