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.
PropTypes = require('prop-types');
  React = require('react');
  ReactDOM = require('react-dom');
  ReactTestUtils = require('react-dom/test-utils');
  
  
  
  jest.resetModuleRegistry();
  require('shared/ReactFeatureFlags').enableReactFragment = true;
  ReactDOMServer = require('react-dom/server');
}
describe('ReactDOMServerIntegration', () => {
  beforeEach(() => {
    resetModules();
    ExecutionEnvironment.canUseDOM = false;
  });
  describe('basic rendering', function() {
    itRenders('a blank div', async render => {
      const e = await render(<div />);
      expect(e.tagName).toBe('DIV');
    });
    itRenders('a self-closing tag', async render => {
      const e = await render(<br />);
      expect(e.tagName).toBe('BR');
    });
    itRenders('a self-closing tag as a child', async render => {
      const e = await render(
        <div>
          <br />
        </div>,