Observed this on react@16.0.0-beta.5

```js
import React from 'react';
import { renderToString } from 'react-dom/server';

const B = () => 'b';

console.log(renderToString(<div>{'a'}<B />{'c'}</div>));
```

This renders as `<div data-reactroot="">a<!-- -->bc</div>`. If you try to hydrate this you'll get the error: Text content did not match. Server: "bc" Client: "b".
return {foo: 'bar'};
          }
        }
        return render(<MyComponent />);
      },
      'MyComponent.getChildContext(): childContextTypes must be defined ' +
        'in order to use getChildContext().',
    );
    itThrowsWhenRendering(
      'if getChildContext returns a value not in childContextTypes',
      render => {
        class MyComponent extends React.Component {
          render() {
            return <div />;
          }
          getChildContext() {
            return {value1: 'foo', value2: 'bar'};
          }
        }
        MyComponent.childContextTypes = {value1: PropTypes.string};
        return render(<MyComponent />);
      },
      'MyComponent.getChildContext(): key "value2" is not defined in childContextTypes.',
    );
  });
  describe('refs', function() {
    it('should not run ref code on server', async () => {
      let refCount = 0;
      class RefsComponent extends React.Component {