Follow up from https://github.com/facebook/react/pull/11616.

Here's one I found. These two invariants:

https://github.com/facebook/react/blob/7e7127387ba64f57299eaff8656542cea6fb3a2d/packages/react-reconciler/src/ReactFiberClassComponent.js#L330-L343

are in a function that's behind a DEV block:

https://github.com/facebook/react/blob/7e7127387ba64f57299eaff8656542cea6fb3a2d/packages/react-reconciler/src/ReactFiberClassComponent.js#L447-L449

I don't think this is intentional, but need to verify.

There may be more. I'll use this issue to track while https://github.com/facebook/react/pull/11616 preserves existing behavior.
);
      expect(e.childNodes.length).toBe(1);
      expect(e.firstChild.tagName).toBe('BR');
    });
    itRenders('a string', async render => {
      let e = await render('Hello');
      expect(e.nodeType).toBe(3);
      expect(e.nodeValue).toMatch('Hello');
    });
    itRenders('a number', async render => {
      let e = await render(42);
      expect(e.nodeType).toBe(3);
      expect(e.nodeValue).toMatch('42');
    });
    itRenders('an array with one child', async render => {
      let e = await render([<div key={1}>text1</div>]);
      let parent = e.parentNode;
      expect(parent.childNodes[0].tagName).toBe('DIV');
    });
    itRenders('an array with several children', async render => {
      let Header = props => {
        return <p>header</p>;
      };
      let Footer = props => {
        return [<h2 key={1}>footer</h2>, <h3 key={2}>about</h3>];
      };
      let e = await render([
        <div key={1}>text1</div>,
        <span key={2}>text2</span>,
        <Header key={3} />,