<!--
  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.


{createNodeMock, foobar: true},
    );
    ReactTestRenderer.create(<Foo />, {createNodeMock});
    ReactTestRenderer.create(<div ref={r => log.push(r)} />);
    ReactTestRenderer.create(<div ref={r => log.push(r)} />, {});
    expect(log).toEqual([
      mockDivInstance,
      mockInputInstance,
      mockListItemInstance,
      mockListItemInstance,
      mockListItemInstance,
      mockAnchorInstance,
      null,
      null,
    ]);
  });
  it('supports unmounting when using refs', () => {
    class Foo extends React.Component {
      render() {
        return <div ref="foo" />;
      }
    }
    const inst = ReactTestRenderer.create(<Foo />, {
      createNodeMock: () => 'foo',
    });
    expect(() => inst.unmount()).not.toThrow();
  });
  it('supports unmounting inner instances', () => {
    let count = 0;
    class Foo extends React.Component {