For consideration.

These warnings are already covered by renderers based on react-reconciler. Maybe we don't gain that much by mirroring them in the shallow renderer? Maybe it's not worth the added complexity? Particularly with more complicated warnings like the ones being added for #12419 and #12404.
componentWillReceiveProps() {}
      componentWillMount() {}
      componentWillUpdate() {}
      render() {
        return null;
      }
    }
    const shallowRenderer = createRenderer();
    expect(() =>
      shallowRenderer.render(<ComponentWithWarnings />),
    ).toLowPriorityWarnDev(
      'Warning: ComponentWithWarnings: componentWillMount() is deprecated and will ' +
        'be removed in the next major version.',
    );
    expect(() =>
      shallowRenderer.render(<ComponentWithWarnings />),
    ).toLowPriorityWarnDev([
      'Warning: ComponentWithWarnings: componentWillReceiveProps() is deprecated ' +
        'and will be removed in the next major version.',
      'Warning: ComponentWithWarnings: componentWillUpdate() is deprecated and will ' +
        'be removed in the next major version.',
    ]);
    
    shallowRenderer.render(<ComponentWithWarnings />);
  });
  describe('react-lifecycles-compat', () => {
    const polyfill = require('react-lifecycles-compat');
    it('should not warn about deprecated cWM/cWRP for polyfilled components', () => {
      class PolyfilledComponent extends React.Component {