This DEV-only field was added in 836331ba5f69f2cc53b273ec073fae116db14302 by @sebmarkbage but it's not being used anymore to my knowledge.
render() {
        return (
          <Indirection>
            <FunctionComponent name="A" ref="stateless" />
          </Indirection>
        );
      }
    }
    expect(() =>
      ReactTestUtils.renderIntoDocument(<ParentUsingStringRef />),
    ).toErrorDev(
      'Warning: Function components cannot be given refs. ' +
        'Attempts to access this ref will fail. ' +
        'Did you mean to use React.forwardRef()?\n\n' +
        'Check the render method ' +
        'of `ParentUsingStringRef`.\n' +
        '    in FunctionComponent (at **)\n' +
        '    in div (at **)\n' +
        '    in Indirection (at **)\n' +
        '    in ParentUsingStringRef (at **)',
    );
    
    ReactTestUtils.renderIntoDocument(<ParentUsingStringRef />);
  });
  it('should warn when given a function ref', () => {
    function Indirection(props) {
      return <div>{props.children}</div>;
    }
    class ParentUsingFunctionRef extends React.Component {