Given the following test case

``` jsx
function TestCmp() {
  return <span>{NaN}</span>;
}

ReactDOM.render(<TestCmp />, document.getElementById('app'));
```

Produces the following warning:

```
Warning: Component's children should not be mutated.
    in span (created by TestCmp)
    in TestCmp (created by Unknown)
```

This is probably caused by [this mutation check](https://github.com/facebook/react/blob/328fc75bc910032ff37dc9d93429fb14b476bd0d/src/renderers/shared/hooks/ReactChildrenMutationWarningHook.js#L34), which was introduced in 15.3.0, but it doesn't work for NaN, because NaN != NaN

return str.replace(/\(at .+?:\d+\)/g, '(at **)');
}
describe('ReactComponent', () => {
  beforeEach(() => {
    React = require('React');
    ReactDOM = require('ReactDOM');
    ReactTestUtils = require('ReactTestUtils');
  });
  it('should throw on invalid render targets', () => {
    var container = document.createElement('div');
    
    expect(function() {
      ReactDOM.render(<div></div>, [container]);
    }).toThrowError(
      '_registerComponent(...): Target container is not a DOM element.'
    );
    expect(function() {
      ReactDOM.render(<div></div>, null);
    }).toThrowError(
      '_registerComponent(...): Target container is not a DOM element.'
    );
  });
  it('should throw when supplying a ref outside of render method', () => {
    var instance = <div ref="badDiv" />;
    expect(function() {
      instance = ReactTestUtils.renderIntoDocument(instance);