anchor.diff:                      top: 300.0,
                       child: new Tooltip(
                         key: key,
  -                      message: 'TIP',
  +                      message: tooltipText,
                         height: 190.0,
                         padding: const EdgeInsets.all(0.0),
                         verticalOffset: 100.0,
  
positive.code:                     top: 300.0,
                      child: new Tooltip(
                        key: key,
                        message: 'TIP',
                        child: new Container(width: 0.0, height: 0.0)
                      )
                    ),
  
negative.code: // It's ok to do this in tests, but you really don't want to do it in
  // production code.
  
  const String tooltipText = 'TIP';
  
  void main() {
    testWidgets('Does tooltip end up in the right place - center', (WidgetTester tester) async {
      GlobalKey key = new GlobalKey();
  