<!--
  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

},
    commitMount(
      instance: Instance,
      type: string,
      newProps: Props,
      internalInstanceHandle: Object,
    ): void {
      
    },
    commitTextUpdate(
      textInstance: TextInstance,
      oldText: string,
      newText: string,
    ): void {
      textInstance.text = newText;
    },
    resetTextContent(testElement: Instance): void {
      
    },
    appendChild: appendChild,
    appendChildToContainer: appendChild,
    insertBefore: insertBefore,
    insertInContainerBefore: insertBefore,
    removeChild: removeChild,
    removeChildFromContainer: removeChild,
  },
});
const defaultTestOptions = {
  createNodeMock: function() {
    return null;