This DEV-only field was added in 836331ba5f69f2cc53b273ec073fae116db14302 by @sebmarkbage but it's not being used anymore to my knowledge.
'Check the render method ' +
        'of `ParentUsingFunctionRef`.\n' +
        '    in FunctionComponent (at **)\n' +
        '    in div (at **)\n' +
        '    in Indirection (at **)\n' +
        '    in ParentUsingFunctionRef (at **)',
    );
    
    ReactTestUtils.renderIntoDocument(<ParentUsingFunctionRef />);
  });
  it('deduplicates ref warnings based on element or owner', () => {
    
    class AnonymousParentUsingJSX extends React.Component {
      render() {
        return <FunctionComponent name="A" ref={() => {}} />;
      }
    }
    Object.defineProperty(AnonymousParentUsingJSX, 'name', {value: undefined});
    let instance1;
    expect(() => {
      instance1 = ReactTestUtils.renderIntoDocument(
        <AnonymousParentUsingJSX />,
      );
    }).toErrorDev('Warning: Function components cannot be given refs.');
    
    instance1.forceUpdate();
    
    ReactTestUtils.renderIntoDocument(<AnonymousParentUsingJSX />);
    
    class AnonymousParentNotUsingJSX extends React.Component {