<!--
  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, I guess

**What is the current behavior?** 


```
  console.error node_modules/fbjs/lib/warning.js:33
    Warning: Detected multiple renderers concurrently rendering the same context provider. This is currently unsupported.
```

Steps to reproduce the behavior:
1. `git clone https://github.com/stereobooster/react-context-issue`
2. `cd react-context-issue`
3. `yarn`
4. `yarn test`

**What is the expected behavior?** no warning

**Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?** React 16.4. Browser not affected, because error is in node.js

Open this because of https://github.com/facebook/react/pull/13127#issuecomment-402527012

Issue happens because of Enzyme (https://github.com/airbnb/enzyme/issues/1693), code is unreleased, so I copy-pasted it from master. 

I'm looking for advice or some clue on how to fix this, so I would be able to create PR in Enzyme repo (or in React repo if this is the case). Thank you.


});
  it('can render and update root fragments', () => {
    const Component = props => props.children;
    const renderer = ReactTestRenderer.create([
      <Component key="a">Hi</Component>,
      <Component key="b">Bye</Component>,
    ]);
    expect(renderer.toJSON()).toEqual(['Hi', 'Bye']);
    renderer.update(<div />);
    expect(renderer.toJSON()).toEqual({
      type: 'div',
      children: null,
      props: {},
    });
    renderer.update([<div key="a">goodbye</div>, 'world']);
    expect(renderer.toJSON()).toEqual([
      {
        type: 'div',
        children: ['goodbye'],
        props: {},
      },
      'world',
    ]);
  });
  it('supports context providers and consumers', () => {
    const {Consumer, Provider} = React.createContext('a');
    function Child(props) {
      return props.value;
    }
    function App() {