*feature*

>Warning: A component is `contentEditable` and contains `children` managed by React. It is now your responsibility to guarantee that none of those nodes are unexpectedly modified or duplicated. This is probably not intentional.

It would help heaps if I would know _which_ component is causing this.
ReactDOM.render(<div is="custom-element" class="bar" />, container);
      expect(container.firstChild.getAttribute('class')).toBe('bar');
    });
  });
  describe('Custom attributes', function() {
    it('allows assignment of custom attributes with string values', function() {
      var el = ReactTestUtils.renderIntoDocument(<div whatever="30" />);
      expect(el.getAttribute('whatever')).toBe('30');
    });
    it('removes custom attributes', function() {
      const container = document.createElement('div');
      ReactDOM.render(<div whatever="30" />, container);
      expect(container.firstChild.getAttribute('whatever')).toBe('30');
      ReactDOM.render(<div whatever={null} />, container);
      expect(container.firstChild.hasAttribute('whatever')).toBe(false);
    });
    it('does not assign a boolean custom attributes as a string', function() {
      spyOn(console, 'error');
      var el = ReactTestUtils.renderIntoDocument(<div whatever={true} />);
      expect(el.hasAttribute('whatever')).toBe(false);
      expectDev(console.error.calls.argsFor(0)[0]).toContain(
        'Warning: Received `true` for non-boolean attribute `whatever`',
      );
    });
    it('does not assign an implicit boolean custom attributes', function() {
      spyOn(console, 'error');
      
      var el = ReactTestUtils.renderIntoDocument(<div whatever />);
      expect(el.hasAttribute('whatever')).toBe(false);
      expectDev(console.error.calls.argsFor(0)[0]).toContain(