render() {
          return (
            <React.unstable_AsyncMode>
              {this.props.foo ? <Foo /> : <Bar />}
            </React.unstable_AsyncMode>
          );
        }
      }
      class Foo extends React.Component {
        UNSAFE_componentWillMount() {}
        render() {
          return null;
        }
      }
      class Bar extends React.Component {
        UNSAFE_componentWillMount() {}