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.
return {foo: 'bar'};
            }
          }
          return render(<MyComponent />);
        },
        'MyComponent.getChildContext(): childContextTypes must be defined ' +
          'in order to use getChildContext().',
      );
    }
    itThrowsWhenRendering(
      'if getChildContext returns a value not in childContextTypes',
      render => {
        class MyComponent extends React.Component {
          render() {
            return <div />;
          }
          getChildContext() {
            return {value1: 'foo', value2: 'bar'};
          }
        }
        MyComponent.childContextTypes = {value1: PropTypes.string};
        return render(<MyComponent />);
      },
      'MyComponent.getChildContext(): key "value2" is not defined in childContextTypes.',
    );
  });
  describe('refs', function() {
    it('should not run ref code on server', async () => {
      let refCount = 0;
      class RefsComponent extends React.Component {