Same as https://github.com/facebook/react/issues/10103, but for the server renderer. You can look at implementation in https://github.com/facebook/react/pull/11168 and do something very similar in `ReactPartialRenderer.js`.
it('should warn about contentEditable and children', () => {
    expect(() =>
      ReactDOMServer.renderToString(<div contentEditable={true} children="" />),
    ).toWarnDev(
      'Warning: A component is `contentEditable` and contains `children` ' +
        'managed by React. It is now your responsibility to guarantee that ' +
        'none of those nodes are unexpectedly modified or duplicated. This ' +
        'is probably not intentional.\n    in div (at **)',
    );
  });
  it('should throw rendering call/return on the server', () => {
    expect(() => {
      ReactDOMServer.renderToString(
        <div>{ReactCallReturn.unstable_createReturn(42)}</div>,
      );
    }).toThrow(
      'The experimental Call and Return types are not currently supported by the server renderer.',
    );
    expect(() => {
      ReactDOMServer.renderToString(
        <div>
          {ReactCallReturn.unstable_createCall(null, function() {}, {})}
        </div>,
      );
    }).toThrow(
      'The experimental Call and Return types are not currently supported by the server renderer.',
    );
  });
});