<!--
  Note: if the issue is about documentation or the website, please file it at:
  https://github.com/reactjs/reactjs.org/issues/new
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**Do you want to request a *feature* or report a *bug*?**
Bug. Behavior regression.

**What is the current behavior?**
Package throws when being required in Node.

**If the current behavior is a bug, please provide the steps to reproduce and if possible a minimal demo of the problem. Your bug will get fixed much faster if we can run your code and it doesn't have dependencies other than React. Paste the link to your JSFiddle (https://jsfiddle.net/Luktwrdm/) or CodeSandbox (https://codesandbox.io/s/new) example below:**

```
avi@localhost  ~/projects/r168  node
> require('react-dom/test-utils')
ReferenceError: document is not defined
    at /home/avi/projects/r168/node_modules/react-dom/cjs/react-dom-test-utils.development.js:944:27
    at Object.<anonymous> (/home/avi/projects/r168/node_modules/react-dom/cjs/react-dom-test-utils.development.js:1283:5)
    at Module._compile (internal/modules/cjs/loader.js:689:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:700:10)
    at Module.load (internal/modules/cjs/loader.js:599:32)
    at tryModuleLoad (internal/modules/cjs/loader.js:538:12)
    at Function.Module._load (internal/modules/cjs/loader.js:530:3)
    at Module.require (internal/modules/cjs/loader.js:637:17)
    at require (internal/modules/cjs/helpers.js:22:18)
```

**What is the expected behavior?**
`react-dom/test-utils` should not throw in "pure" node (without `jsdom` providing fake document on global).

**Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?**
happens on 16.8.0
previous versions work.
componentWillUnmount() {
        count++;
      }
      render() {
        return <div />;
      }
    }
    const inst = ReactTestRenderer.create(
      <div>
        <Foo />
      </div>,
      {
        createNodeMock: () => 'foo',
      },
    );
    expect(() => inst.unmount()).not.toThrow();
    expect(count).toEqual(1);
  });
  it('supports updates when using refs', () => {
    const log = [];
    const createNodeMock = element => {
      log.push(element.type);
      return element.type;
    };
    class Foo extends React.Component {