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".
it(`renders ${desc} with clean client render`, () =>
    testFn(clientCleanRender));
  it(`renders ${desc} with client render on top of good server markup`, () =>
    testFn(clientRenderOnServerString));
  it(`renders ${desc} with client render on top of bad server markup`, async () => {
    try {
      await testFn(clientRenderOnBadMarkup);
    } catch (x) {
      
      if (!(x instanceof BadMarkupExpected)) {
        
        throw x;
      }
    }
  });
}
function itThrows(desc, testFn, partialMessage) {
  it(`throws ${desc}`, () => {
    return testFn().then(
      () => expect(false).toBe('The promise resolved and should not have.'),
      err => {
        expect(err).toBeInstanceOf(Error);
        expect(err.message).toContain(partialMessage);
      },
    );
  });
}
function itThrowsWhenRendering(desc, testFn, partialMessage) {