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.
render() {
            return <div>foo</div>;
          }
        }
        checkFooDiv(await render(<ClassComponent />));
      });
      itRenders('factory components', async render => {
        const FactoryComponent = () => {
          return {
            render: function() {
              return <div>foo</div>;
            },
          };
        };
        checkFooDiv(await render(<FactoryComponent />));
      });
    });
    describe('component hierarchies', async function() {
      itRenders('single child hierarchies of components', async render => {
        const Component = props => <div>{props.children}</div>;
        let e = await render(
          <Component>
            <Component>
              <Component>
                <Component />
              </Component>
            </Component>
          </Component>,
        );