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".
expect(e.getAttribute('hidden')).toBe('');
      });
      
      
      
      itRenders('boolean prop with "" value', async render => {
        const e = await render(<div hidden="" />);
        expect(e.getAttribute('hidden')).toBe(null);
      });
      
      itRenders('boolean prop with string value', async render => {
        const e = await render(<div hidden="foo" />);
        expect(e.getAttribute('hidden')).toBe('');
      });
      
      itRenders('boolean prop with array value', async render => {
        const e = await render(<div hidden={['foo', 'bar']} />);
        expect(e.getAttribute('hidden')).toBe('');
      });
      
      itRenders('boolean prop with object value', async render => {
        const e = await render(<div hidden={{foo: 'bar'}} />);
        expect(e.getAttribute('hidden')).toBe('');
      });
      
      itRenders('boolean prop with non-zero number value', async render => {
        const e = await render(<div hidden={10} />);
        expect(e.getAttribute('hidden')).toBe('');
      });