Class B

packages/react-dom/src/__tests__/ReactUpdates-test.js:698–704

    }

    class B extends React.Component {
      state = {x: 0};

      render() {
        return <div>B{this.state.x}</div>;
      }
    }

    const container = document.createElement('div');
    const root = ReactDOMClient.createRoot(container);